How long in the sun
How long in the sun for vitamin D with brown or dark skin
You need several times longer than the figure that circulates, and at high latitudes the sun may not be able to supply it at all.
Between 19 and 72 minutes, depending on the month.
Why deficiency is more common far from the equator
Melanin is effective sun protection, and it protects against the same wavelength that makes the vitamin. That is an advantage where the sun is strong and a disadvantage where it is weak: skin evolved for equatorial light gets a fraction of the yield from a northern winter. Health services single this out — the NHS names people of African, African-Caribbean and South Asian background as more likely to run low, and the reason is arithmetic, not behaviour. The practical consequence is that the shoulder months close earlier for you than the calendar suggests, and the months this page marks impossible are impossible however long you stay out.
Fitzpatrick V and VI: skin that rarely or never burns and tans deeply.
What these numbers assume
- 25% of your skin uncovered — roughly arms and face
- age 35, because synthesis slows as skin ages
- a target of 1000 IU in one session
- latitude 40°, clear sky, at sea level
1000 IU is this tool's choice, not a settled consensus: national bodies recommend anywhere from 600 to 2000 IU a day, and which one you pick changes every number on this page.
Month by month
The quickest and slowest of the band, on the strongest and weakest day of each month.
- January: not possible at any length of exposure
- February: 46–94 min
- March: 29–72 min
- April: 22–46 min
- May: 19–35 min
- June: 19–31 min
- July: 19–31 min
- August: 19–36 min
- September: 23–52 min
- October: 33–90 min
- November: 57–95 min
- December: not possible at any length of exposure
The months when no amount of sun works
At this latitude the sun does not climb high enough in January, December. That is not a matter of staying out longer: below a UV index of 3 the wavelength that makes vitamin D barely reaches the ground at all, so the answer is the same at five minutes and at five hours.
How this compares with burning
On the strongest day of the season you need about 19 min, against roughly 77 min to reach visible redness. The vitamin D is done long before the damage starts — which is the point: there is nothing to gain by staying out until you burn.
The six types in detail
- Type 1: 5–12 min
- Type 2: 6–15 min
- Type 3: 7–18 min
- Type 4: 11–27 min
- Type 5: 19–45 min
- Type 6: 30–72 min
Not your skin?
You need the least, and your margin before burning is the shortest.
Type 1–2: 5–15 min
The band the generic advice was written for, unlabelled.
Type 3–4: 7–27 min
Where the numbers come from
Solar elevation is computed for each day of the year, the UV index from it using the Madronich model with van Heuklon's ozone column, and the exposure time from Holick and Dowdy (2010) with the photodegradation ceiling that makes long sessions stop paying. Nothing here is typed in by hand — change the model and this page changes with it.
This is an estimate for a clear sky at a stated latitude, not medical advice, and it cannot know your skin, your medication or your blood levels. If you think you are deficient, that is a question for a doctor and a blood test, not for a calculator.