UV Index Tan Time Calculator: How Long Can You Tan?
How long unprotected skin takes to start reddening, by UV index and skin type — using the live index for your location, or one you set yourself. Shown as a range, because the threshold varies up to fourfold between people of the same type.
This tool provides an informational estimate and is not a substitute for professional medical diagnosis. It does not assess your skin and cannot rule out any condition.
The short answer
How long can you stay in the sun today?
It depends on two numbers and one honest caveat. The first number is the UV index where you are, which changes with the hour, the season and your latitude. The second is how readily your skin reddens, summarised by its Fitzpatrick type. Put them together and you get an estimate of how long unprotected skin takes to reach the dose at which redness begins — at UV 6, that is roughly 15–35 min for the palest skin and 45–70 min for mid-brown skin.
The caveat is that this is a threshold for visible damage, not for damage as such. Ultraviolet breaks DNA bonds well below the dose that turns skin pink, and the redness itself usually appears hours later, when the exposure is long over. So the figure above is useful for planning shade and sunscreen. It is not a budget to spend down, and this page does not present it as one.
The method
How this is calculated
One UV Index unit equals 0.025 W/m² of erythemally weighted irradiance — the constant ker = 40 m²/W defined in the WHO, WMO, UNEP and ICNIRP guide Global Solar UV Index: A Practical Guide. Over a minute that delivers 1.5 J/m², so:
minutes = MED ÷ (1.5 × UV index)
MED is the Minimal Erythemal Dose — the exposure at which skin begins to redden. The point values come from Shih et al., Journal of Investigative Dermatology 2018;138(10):2244–52, the one study that measured all six Fitzpatrick types in erythemally weighted units in a single laboratory: 210, 260, 320, 560, 750 and 1520 J/m².
Those are published study values, measured in six or seven volunteers per type. They describe the group, not you: your own threshold may sit well above or below the figure for your Fitzpatrick type, and nothing short of phototesting can tell you where.
We publish a range rather than a single number because IARC Monograph 100D reports roughly a fourfold spread in MED within one population. Two people of the same Fitzpatrick type can differ more than two adjacent types differ from each other, so a single-minute answer would be false precision.
Sunscreen is not a time multiplier
Labelled SPF is measured with sunscreen applied at 2 mg/cm² (ISO 24444; FDA 21 CFR 201.327). People typically apply 0.4–1.0 mg/cm², and protection falls off exponentially rather than linearly with thickness — SPF(x/2) for x mg/cm², per Faurschou & Wulf, British Journal of Dermatology 2007;156:716–19. Applied the way it usually is, an SPF 30 product therefore delivers far less protection than its label — modelling from that relationship puts it in the single digits rather than at 30. How much less depends on how thickly it went on, which nobody measures in practice, so this tool works from that reduced estimate and shows the label value beside it. Treat the reduced figure as an estimate, not a measurement. As the FDA puts it plainly: “SPF does not reflect time in the sun.”
Reference
UV index and time to reddening, by skin type
Unprotected skin, clear sky, horizontal surface, no reflection from water, sand or snow. Ranges span the published clinical MED bounds. Every figure is an approximation for a group, not a limit for a person: individual thresholds vary considerably within a single Fitzpatrick type. None of these times is a safe period in the sun, and none is a recommended time to tan. Swipe the table sideways for types IV–VI.
| UV index | Type I | Type II | Type III | Type IV | Type V * | Type VI * |
|---|---|---|---|---|---|---|
| 1 Low | 100 min – 3+ h | 170 min – 3+ h | 3+ hours | 3+ hours | 3+ hours | 3+ hours |
| 2 Low | 50–100 min | 80–130 min | 100–170 min | 130 min – 3+ h | 3+ hours | 3+ hours |
| 3 Moderate | 35–70 min | 55–90 min | 70–110 min | 90–130 min | 130 min – 3+ h | 3+ hours |
| 4 Moderate | 25–50 min | 40–70 min | 50–80 min | 70–100 min | 100–150 min | 150 min – 3+ h |
| 5 Moderate | 20–40 min | 35–55 min | 40–70 min | 55–80 min | 80–120 min | 120 min – 3+ h |
| 6 High | 15–35 min | 30–45 min | 35–55 min | 45–70 min | 70–100 min | 100–170 min |
| 7 High | 15–30 min | 25–40 min | 30–50 min | 40–55 min | 55–90 min | 90–140 min |
| 8 Very high | 15–25 min | 20–35 min | 25–40 min | 35–50 min | 50–80 min | 80–130 min |
| 9 Very high | 10–20 min | 20–30 min | 20–35 min | 30–45 min | 45–70 min | 70–110 min |
| 10 Very high | 10–20 min | 15–25 min | 20–35 min | 25–40 min | 40–60 min | 60–100 min |
| 11 Extreme | 9–20 min | 15–25 min | 20–30 min | 25–35 min | 35–55 min | 55–90 min |
* Types V and VI are marked low-confidence: most phototesting studies enrol few or no participants with deeply pigmented skin, so those figures rest on thinner evidence than the rest of the table.
Background
What is the UV index?
The UV index is a measure of the strength of sunburn-causing ultraviolet radiation at ground level. It is not a temperature and not a measure of brightness — it is irradiance weighted by how effectively each wavelength reddens human skin, then multiplied by a fixed constant of 40 m²/W. One index unit corresponds to 0.025 W/m² of that erythemally weighted energy.
The scale starts at zero and has no formal ceiling. Readings above 11 occur at high altitude, near the equator and over snow or water, which reflect ultraviolet back at you. The World Health Organization groups the scale into five exposure categories, and its advice is deliberately binary rather than graduated: below 3, protection is not normally needed; at 3 and above it is, whatever your skin type; at 8 and above the same message is reinforced more strongly.
One consequence of the definition is worth spelling out, because it is the single most useful thing to know about the index: because it is a rate, doubling it halves the time to any given dose. Whatever your skin does at UV 4, it does twice as fast at UV 8.
Skin types
Fitzpatrick skin types and sun sensitivity
The Fitzpatrick scale, published by Thomas Fitzpatrick in 1975 and revised in 1988, classifies skin by how it reacts to sun rather than by how it looks. It was designed to help set phototherapy doses, and it does that job by asking two questions: does this skin burn, and does it tan?
Always burns, never tans. Pale skin, often freckles.
Usually burns, tans minimally. Fair skin.
Sometimes burns, tans gradually. Light-olive skin.
Rarely burns, tans easily. Olive or mid-brown skin.
Very rarely burns, tans deeply. Brown skin.
Very rarely burns. Deeply pigmented brown to black skin.
Two limitations matter enough to state plainly. The scale was built around lighter skin — types V and VI were added later, and most phototesting studies since have enrolled few or no participants with deeply pigmented skin, which is why the last two columns of our table rest on thinner evidence. And measured thresholds overlap heavily between neighbouring types: two people who answer the questionnaire differently can have the same erythemal threshold, and two people of the same type can differ from each other by more than the gap between types. Fitzpatrick type is a useful shorthand. It is not a measurement of your skin.
On sunscreen, the practical guidance does not vary much by type. Broad-spectrum SPF 30 or higher, applied generously and reapplied at least every two hours, is the standard advice across all six. Darker skin is not exempt: it burns less readily, but melanoma in deeply pigmented skin is typically found at a later stage and carries a worse outcome, which makes noticing change more important, not less.
By UV level
How long can you tan at each UV index, from 3 to 10?
Below is every level most people actually meet, from the threshold at which protection starts to matter to the readings found at altitude and near the equator. Each strip shows all six Fitzpatrick types at that index, unprotected, under a clear sky — and every figure is generated from the same model as the reference table above, so the numbers in this text cannot drift away from it.
How long does it take to tan in UV 3?
UV 3 is where the World Health Organization starts recommending protection, and the choice of that number is deliberate: below it, even very fair skin is unlikely to accumulate a meaningful dose over an ordinary day. You will meet UV 3 around noon in northern Europe in spring and early autumn, and through much of a British summer. It is the quietest level at which sunburn is still a realistic outcome if you stay out long enough.
Tanning at this level is slow, which is exactly what makes it deceptive. The dose arrives too gradually to prompt anyone to seek shade, so UV 3 is the index at which habitual daily exposure — a lunch break, a commute, a garden — quietly does most of its lifetime work. A shirt and midday shade cover it for most people; the strongest case for sunscreen is on the face and the backs of the hands, which take the exposure every single day.
Can you tan in UV 4?
UV 4 sits in the middle of the moderate band and is typical of a clear late-spring day across temperate Europe and the northern United States. It is worth knowing that a UV index quoted for a day is almost always its peak, reached within an hour or two of solar noon; at nine in the morning the same day might be running at a third of that.
This is the level at which the shadow rule earns its keep. If your shadow is shorter than you are, the sun is high enough that the index is near its daily maximum and the figures below apply; if your shadow is longer than you are, the real rate is lower and you have more time than the strip suggests. Yes, skin tans at UV 4 — but the pigment is a response to DNA damage that has already happened, not a shield being raised in advance.
Is UV 5 safe to tan in?
UV 5 is the top of the moderate band, and the level at which a temperate summer spends most of its afternoons. Nothing about the physics changes here — the rate is simply higher, so every margin narrows. An hour of inattention at UV 5 is enough to redden most fair skin, where the same hour at UV 3 would not have been.
The honest answer to whether it is safe to tan is that no UV level makes tanning free. The pigment appears because repair machinery has been triggered inside skin cells; it is the visible end of a damage response, not evidence that damage was avoided. What UV 5 does change is the size of the mistake you can make: at this index, the difference between a pleasant afternoon and a burn is roughly the length of one film.
How long does it take to tan in UV 6?
UV 6 opens the high band. It is a Mediterranean spring, a Californian or continental-American summer, and any clear midsummer day in southern Europe. Because the index is a rate, UV 6 delivers a given dose in exactly half the time UV 3 does — the times in the strip below are half those in the UV 3 section, and that halving is the single most useful thing to carry away from this page.
At this level surroundings start to matter as much as the number. Sand, water and pale concrete reflect ultraviolet upward, so a beach at UV 6 delivers more than a lawn at UV 6, and a parasol protects noticeably less on the beach than it does on grass. Tanning here is quick enough that people mistake speed for safety; in practice the visible pigment lags the exposure by a day or two, which means the tan you see on Tuesday reports Sunday.
How long does it take to burn at UV 7?
UV 7 is the top of the high band — Mediterranean or Californian summer around solar noon, and a common reading on clear days in the subtropics. This is the point at which the binding constraint stops being your skin and starts being your sunscreen: reapplication every two hours matters more than any timer, because the product degrades, rubs off and washes away long before the day does.
It is also where the base-tan myth does its damage. A tan acquired deliberately provides an estimated protection factor of only about two to four — the equivalent of a very weak sunscreen — while carrying the full DNA cost of the exposure that produced it. Preparing for a holiday by tanning first buys almost nothing and pays for it twice. Shade through the middle of the day is worth more than any amount of pre-exposure.
Can you tan safely at UV 8?
UV 8 begins the very high band, and it is where the WHO reinforces its message rather than merely repeating it. Expect it in the subtropics, in mountains during summer, and across southern Europe in July and August. At this rate the reddening threshold for the fairest skin arrives at about a quarter of an hour, and the practical advice shifts from managing time to avoiding the hours entirely.
The ordering of protection also inverts here. Below UV 6, sunscreen can reasonably carry most of the load; from UV 8 upward, clothing, a wide-brimmed hat and genuine shade do the heavy work, because no realistic application of sunscreen keeps pace with this rate for an afternoon. Deeply pigmented skin has more room at this level, but it is not exempt: the dose still accumulates, and melanoma found later in darker skin carries a worse outcome.
How long does it take to burn at UV 9?
UV 9 is a tropical midday, a high plateau, or a clear summer noon in the deep subtropics. The numbers below get small enough that the question changes shape: once the fairest skin is reaching its threshold in a quarter of an hour, a countdown is no longer a useful way to plan, because the interval is shorter than the time it takes to notice you have been out too long.
What replaces the timer is planning the day rather than the hour. The three or four hours either side of solar noon carry a disproportionate share of the total dose, so moving activity to the morning or the evening removes more exposure than any product can. Tanning at UV 9 is fast, and the speed is the warning: the rate that darkens skin in an afternoon is the same rate that reddens it in minutes.
Is it safe to tan at UV 10?
UV 10 sits at the top of the very high band, one step below extreme. It occurs near the equator, at altitude — ultraviolet climbs as the atmosphere above you thins — and over surfaces that reflect it back, which is why fresh snow in cold mountain air produces some of the most severe sunburn people ever experience. Temperature is no guide at all: the air can be freezing while the index is at its worst.
Reflection is the reason this level deserves separate treatment. Snow can send a large fraction of incident ultraviolet back upward, in effect adding a second sun that reaches the underside of the chin, the nose and the eyelids — places clothing does not cover and sunscreen is rarely reapplied. At UV 10 even the deepest skin types reach the reddening threshold within about an hour, and no skin type has a version of this level that is safe to tan in.
Reality check
What changes your real burn time
The model assumes a clear sky, a horizontal surface, untanned skin and no reflection. Real conditions move the answer in both directions, sometimes by more than the difference between two skin types.
- Reflection. Fresh snow can reflect a large fraction of incident ultraviolet back at you, effectively adding a second sun; water, white sand and concrete reflect less but still meaningfully. Shade from a parasol on a beach protects far less than the same parasol on grass.
- Altitude. Ultraviolet increases with elevation as the atmosphere above you thins — which is why mountain sunburn in cold air is a common surprise. Temperature is not a cue for UV.
- Cloud. Cloud attenuates ultraviolet much less than it attenuates warmth and glare, so an overcast day can feel mild while the index stays high. Broken cloud can briefly push ground-level UV above the clear-sky value through scattering.
- Time of day. The index quoted for a day is usually its peak. Away from solar noon the actual rate is lower, sometimes far lower, which is why this tool asks for the current index rather than the daily maximum.
- Medication and health conditions. Some antibiotics, diuretics, retinoids, NSAIDs and St John's wort are photosensitising and can reduce the erythemal threshold sharply. Several skin conditions do the same. If you take regular medication, check the label rather than this page.
- Previous exposure. Skin that has already tanned this season tolerates more than untanned skin. The model assumes untanned, so it errs toward caution for people mid-summer and is about right in spring.
Protection
Sun safety: what protection actually does
Every public health body converges on the same ordering, and it is not the one most people assume. Shade and clothing come first because they are not application-dependent; sunscreen comes last because its real-world performance depends entirely on how much of it is on your skin and how long it has been there.
A shirt, a wide-brimmed hat and sunglasses remove most of the exposure to the areas that receive the highest cumulative dose over a lifetime. Timing removes more: the hours either side of solar noon carry a disproportionate share of the day's total. Sunscreen then covers what is left — broad-spectrum, SPF 30 or above, applied generously and reapplied at least every two hours and after swimming, sweating or towelling.
What sunscreen should not do is buy time. The whole reason this calculator refuses to multiply your result by the SPF number is that doing so converts a protective measure into a permission slip, which is precisely how sunscreen ends up increasing total exposure rather than reducing it.
The myth
Does a base tan protect you?
It does something, and the something has been measured. Two weeks of daily suberythemal exposure raised the erythemal threshold by a factor of 1.4 to 2.1 in skin types II and III — an induced protection factor, measured the same way this page measures everything else, as a ratio of doses. At UV 6 that moves type II from about 30–45 min to roughly 60–90 min.
Put beside the alternatives, that is the whole case against the idea. A tan earned over a fortnight of deliberate exposure buys less than a poorly applied sunscreen: applied as thinly as people actually apply it, an SPF 30 product still delivers several times more protection than a tan does. A shirt does more than either, and costs nothing.
A tan acquired under UVA alone — a sunbed, or the “gentle” end of a spring afternoon — contributes essentially no photoprotection at all. UVA darkens pigment that is already there by oxidising it, without the melanin synthesis and stratum-corneum thickening that do the protecting. The colour looks the same in the mirror and is worth nothing on the skin.
And the protection is against reddening, not against risk. The pigment exists because DNA was damaged and repair was triggered; every kind of UV-induced tan carries that damage. Buying a factor of two against sunburn by accumulating the exact injury that sunburn is a warning about is not a trade worth making.
Why it matters
Sun exposure and skin cancer risk
Ultraviolet radiation is classified by the International Agency for Research on Cancer as a Group 1 carcinogen — the same category as tobacco smoke and asbestos. The mechanism is cumulative: each exposure adds DNA damage, most of which is repaired, and the small unrepaired fraction accumulates over decades. This is why the absence of sunburn is not the same as the absence of harm, and why a reddening-time estimate is a poor proxy for risk.
That risk is not spread evenly. The WHO guide reports that more than 90% of non-melanoma skin cancers occur in skin types I and II, which is why its own advice is aimed first at fair skin that burns. The same paragraph carries the qualifier that usually gets dropped when the figure is repeated: incidence is lower in dark-skinned people, but they remain susceptible to UV damage — particularly to the eyes and the immune system. A low number in a statistic is not an exemption, and melanoma in deeply pigmented skin is typically found later and carries a worse outcome.
What changes outcomes is noticing change early. A mole or patch that grows, changes colour, develops an irregular edge, itches, bleeds or simply looks different from your others is worth showing to a doctor, regardless of how much sun you think you have had.
Our dermatology atlas covers the conditions most closely linked to cumulative sun exposure: Melanoma, Actinic keratosis, Lentigo Melanoma.
Honest caveat
Why the WHO advises against “burn time” calculators
“Burn times have been used in many countries as this simple concept can be directly translated into action. However, people tend to interpret burn times to mean that there is a safe level of unprotected sun exposure. Hence, relating UVI values to “time to burn” or “safe tanning time” sends out the wrong message to the public.”
WHO / WMO / UNEP / ICNIRP, Global Solar UV Index: A Practical Guide
The objection is about how people read the number, not about the arithmetic. A burn time reads as permission — a budget you can spend before protection matters. It is not one.
That is why this page leads with the threshold rather than the countdown: above UV 3, protection is needed regardless of skin type, and the guidance is reinforced at UV 8 and above.
Australia makes the point most plainly. ARPANSA runs the country with the highest ultraviolet levels in the world, publishes the same five exposure categories we use, and classifies skin by Fitzpatrick type — and still states its advice as a dose, in Standard Erythemal Dose, never as minutes. Its site carries no burn-time figure at all.
We publish the estimate anyway, as a range and with its assumptions visible, because people search for it and the alternative is that they find one of the many tools that present a single confident number with no sources and no caveats.
Questions
Frequently asked questions
How long can I stay in the sun without burning?
There is no exposure that carries no risk, so the honest answer is a range rather than a number. At UV 6, unprotected skin of Fitzpatrick type I typically begins to redden after 15–35 min, while type IV has roughly 45–70 min. Those bounds come from published Minimal Erythemal Dose values, and individual thresholds vary up to fourfold within a single skin type — which means two people who would answer the Fitzpatrick questionnaire identically can differ by more than the gap between two adjacent types. Above UV 3, protection is advised whatever your skin type.
How does the UV index affect tanning time?
Inversely and proportionally. One UV Index unit delivers 1.5 J/m² of erythemally weighted energy per minute, so doubling the index halves the time to any given dose. Going from UV 4 to UV 8 cuts the time to reddening exactly in half, and the same relationship holds for the dose that produces a tan. This is why a single figure quoted without its UV index is meaningless, and why the times on this page are always shown against a specific level rather than as general advice.
What UV index is safe for tanning?
None of them, in the sense people usually mean. The WHO treats UV 3 as the threshold above which protection is needed, and states explicitly that relating UV index values to a "safe tanning time" sends the wrong message to the public. Tanning is itself a response to DNA damage — melanin is produced because repair machinery has been triggered — so there is no level at which the pigment arrives without a cost having been paid first. What changes between levels is how quickly that cost accrues, not whether it does.
What UV index is best for tanning?
The question has no good answer, because the same radiation that produces pigment produces the damage. There is no wavelength band, index value or time of day at which one happens without the other, and no evidence that a slow tan is biologically cheaper than a fast one for the same total dose. If the aim is colour without exposure, a topical product is the only route that carries no ultraviolet cost at all. If the aim is time outdoors, the useful question is not which index is best but how to keep the dose low at whatever index the day brings.
Does a base tan protect you?
Barely, and not in the way the phrase implies. Measured as the ratio of erythemal thresholds before and after two weeks of daily suberythemal exposure, an acquired tan raised the threshold by a factor of 1.4 to 2.1 in skin types II and III (Sheehan et al. 1998). At UV 6 that moves type II from about 30–45 min to roughly 60–90 min — real, but a fraction of what any sunscreen does, and paid for with the DNA damage that produced the pigment in the first place. A tan acquired under UVA alone, as in a sunbed, contributes essentially no photoprotection at all (Miyamura et al. 2011). Whatever protection exists is against reddening, not against skin cancer risk.
Does SPF 30 give me 30 times longer in the sun?
No. SPF is a ratio of doses measured with sunscreen applied at 2 mg/cm², while people typically apply between 0.4 and 1.0 mg/cm². Protection falls off exponentially rather than linearly with thickness, so applied the way it usually is, an SPF 30 product delivers far less than its label — published modelling puts it in the single digits rather than at 30. The exact figure depends on how thickly it went on and cannot be known for any one person, so this calculator uses that reduced estimate and shows the label value beside it. The FDA states plainly that SPF does not reflect time in the sun: sunscreen should reduce the dose you receive, not extend the time you stay out.
Does sunscreen prevent tanning?
It reduces tanning in proportion to how much it reduces the dose, but it does not prevent it, and in practice it prevents far less than the label implies. Because most people apply roughly a third to a half of the tested amount, miss areas entirely and let the film degrade over hours, a substantial share of the ultraviolet still arrives. The perverse result is well documented: people who apply sunscreen often stay out longer, and end up with both a tan and a higher total dose than they would have received without it.
What is MED, or Minimal Erythemal Dose?
MED is the smallest ultraviolet dose that produces just-perceptible redness with clearly defined borders, assessed 16 to 24 hours after exposure. It is measured in joules per square metre of erythemally weighted energy, and it is the quantity this calculator divides by to produce a time. Published values for the six Fitzpatrick types run from roughly 210 J/m² to 1520 J/m². Two cautions matter: MED is an individual biological threshold rather than a property of a category, and values quoted from narrowband-UVB phototherapy are on a different scale entirely and cannot be used here.
Can you get sunburned on a cloudy day?
Yes, and cloud is one of the more reliable ways to be caught out. Cloud attenuates ultraviolet far less than it attenuates visible light and warmth, so the sky can look grey and feel mild while the index stays high. Broken cloud can briefly push ground-level ultraviolet above the clear-sky value through scattering from cloud edges. The practical rule is that neither brightness nor temperature is a cue for ultraviolet: only the index is, which is why this tool reads the live value for your location rather than asking how sunny it feels.
How long does it take to burn at UV 3?
At UV 3, unprotected type I skin reaches the reddening threshold in about 35–70 min, type III in 70–110 min, and type VI in 3+ hours. UV 3 is the level at which the WHO begins recommending protection, and it is the lowest index at which sunburn is a realistic outcome over an ordinary afternoon. Because the dose arrives slowly at this level, it is also the index that does most of the quiet cumulative work over a lifetime of lunch breaks and commutes.
How long does it take to burn at UV 4?
At UV 4 the model puts the onset of reddening at roughly 25–50 min for type I, 50–80 min for type III and 100–150 min for type V, unprotected and under a clear sky. Remember that a UV index quoted for a day is usually its peak, reached within an hour or two of solar noon. If your shadow is longer than you are, the actual rate is lower than these figures assume and you have more time than they suggest.
How long does it take to tan in UV 5?
UV 5 sits at the top of the moderate band. Type I skin reaches the reddening threshold in about 20–40 min, type II in 35–55 min and type IV in 55–80 min. Visible tanning takes longer than reddening does and lags the exposure by a day or two, which is why the tan you notice on a Tuesday reports the dose you took on Sunday. The pigment is the tail end of a repair response, not protection acquired in advance.
How long does it take to burn at UV 6?
At UV 6, unprotected skin reaches the reddening threshold in about 15–35 min for type I, 35–55 min for type III and 100–170 min for type VI. UV 6 opens the high band and delivers any given dose in exactly half the time UV 3 does. Surroundings begin to matter here too: sand, water and pale concrete reflect ultraviolet upward, so a beach at UV 6 delivers more than a lawn at the same index.
How long does it take to burn at UV 7?
At UV 7 the model puts the onset of reddening at roughly 15–30 min for type I, 30–50 min for type III and 55–90 min for type V, unprotected. UV 7 is the top of the high band, typical of Mediterranean or Californian summer around solar noon. At this level the binding constraint stops being your skin and becomes your sunscreen: reapplication every two hours matters more than any countdown, because the film degrades long before the day does.
How long does it take to burn at UV 8?
At UV 8 the fairest skin reaches the reddening threshold in about 15–25 min, type III in 25–40 min and type VI in 80–130 min. UV 8 opens the very high band, where the WHO reinforces rather than merely repeats its advice. The practical shift at this level is that clothing, a wide-brimmed hat and genuine shade do the heavy work, because no realistic application of sunscreen keeps pace with this rate across a whole afternoon.
How long does it take to burn at UV 9?
At UV 9 type I skin reaches the threshold in roughly 10–20 min, type IV in 30–45 min and type VI in 70–110 min. Once the interval for the fairest skin is shorter than the time it takes to notice you have been out too long, a countdown stops being a useful way to plan. Moving activity to the morning or the evening removes more exposure at this level than any product applied at noon.
What is my Fitzpatrick skin type?
Fitzpatrick type describes how your skin reacts to sun rather than what colour it is: type I always burns and never tans, type VI very rarely burns. The scale was published in 1975 and revised in 1988 to help set phototherapy doses. Two limitations are worth stating: it was built around lighter skin, with types V and VI added later and still thinly represented in phototesting studies; and measured thresholds overlap heavily between neighbouring types. Self-assessment is approximate, which is one reason this calculator reports a range rather than a single figure.
When should I reapply sunscreen?
At least every two hours, and immediately after swimming, sweating or towelling — that is the standard guidance from the FDA and dermatology bodies, and it is why this tool caps any result involving sunscreen at two hours. The reasoning is mechanical rather than chemical: the film thins through contact with clothing, towels and water long before the filters themselves are exhausted. The first reapplication matters most, because the initial application is almost always thinner than the label assumes.
Does snow or water reflection increase UV exposure?
Substantially. Fresh snow reflects a large fraction of incident ultraviolet back upward, in effect adding a second source that reaches the underside of the chin, the nose and the eyelids — exactly the places clothing does not cover and sunscreen is rarely reapplied. Water, white sand and pale concrete reflect less but still meaningfully, which is why a parasol on a beach protects noticeably less than the same parasol on grass. None of this is captured by the UV index itself, which is defined on a horizontal surface with no reflection.
Do medications increase sun sensitivity?
Several classes do, sometimes dramatically. Some antibiotics, diuretics, retinoids, non-steroidal anti-inflammatories and St John's wort are photosensitising and can lower the erythemal threshold well below the population values this calculator uses. A number of skin conditions have the same effect. If you take regular medication, the patient information leaflet is the authority here, not this page — and the times shown above should be treated as upper bounds that may not apply to you at all.
Is this tan-time calculator medically accurate?
It is an informational estimate, not a medical assessment. It applies published population-level dose values to the UV index you enter, assuming clear sky, a horizontal surface, untanned skin and no reflection from water, sand or snow. It does not know your medication, your health conditions, your previous exposure this season or your individual threshold, and it cannot rule out any skin condition. The formula, the constants and their sources are published on this page so you can check the arithmetic yourself.
Provenance
Sources and references
Every number this page produces traces to one of the following. Where sources disagree — and on Minimal Erythemal Dose they disagree substantially — we show a range rather than picking a favourite.
- Open-Meteo. Open-Meteo Weather Forecast API. open-meteo.com, 2026. Current UV index and daily maximum for your location, used when you choose to share it. Licensed CC BY 4.0.
- World Health Organization, WMO, UNEP and ICNIRP. Global Solar UV Index: A Practical Guide. World Health Organization, 2002. Definition of the index, the constant k_er = 40 m²/W, the five exposure categories, and the recommendation against reporting burn times.
- Shih BB, Farrar MD, Cooke MS, et al.. Fractional sunburn threshold UVR doses generate equivalent vitamin D and DNA damage in skin types I–VI but with epidermal DNA damage gradient correlated to skin darkness. Journal of Investigative Dermatology, 2018. The Minimal Erythemal Dose values used for all six skin types.
- International Agency for Research on Cancer. Monograph 100D: Solar and Ultraviolet Radiation. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, 2012. The fourfold within-population spread in erythemal threshold, and the classification of UV radiation as a Group 1 carcinogen.
- Faurschou A, Wulf HC. The relation between sun protection factor and amount of sunscreen applied in vivo. British Journal of Dermatology, 2007. The exponential relationship between applied thickness and effective protection.
- Petersen B, Wulf HC. Application of sunscreen — theory and reality. Photodermatology, Photoimmunology & Photomedicine, 2014. Observed real-world application of 0.4–1.0 mg/cm² against the 2 mg/cm² used in testing.
- US Food and Drug Administration. Labeling and effectiveness testing: sunscreen drug products, 21 CFR 201.327. Code of Federal Regulations, 2011. The definition of SPF as a ratio of doses tested at 2 mg/cm², and the statement that SPF does not reflect time in the sun.
- US Environmental Protection Agency. A Guide to the UV Index. US Environmental Protection Agency, 2004. The exposure categories and the section headed “Reporting Burn Times Not Recommended”.
- Sheehan JM, Potten CS, Young AR. Tanning in human skin types II and III offers modest photoprotection against erythema. Photochemistry and Photobiology, 1998. The induced protection factor of an acquired tan, measured as the ratio of erythemal thresholds before and after two weeks of daily exposure.
- Miyamura Y, Coelho SG, Schlenz K, et al.. The deceptive nature of UVA tanning versus the modest protective effects of UVB tanning on human skin. Pigment Cell & Melanoma Research, 2011. UVA-induced tanning contributes essentially no photoprotection, while every kind of UV-induced tan carries DNA and cellular damage. Linked to the free full text rather than the publisher paywall.
- Australian Radiation Protection and Nuclear Safety Agency. Ultraviolet radiation exposure and dose explained. ARPANSA, 2024. Australian guidance stated in Standard Erythemal Dose rather than in minutes, alongside the same five UV Index exposure categories.
Last updated: . Checked against the sources above.
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Board-Certified Dermatologist · Fellow of the American Academy of Dermatology (FAAD)
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