How long in the sun
How long in the sun for vitamin D with medium or olive skin
The advice you have already read was written for you. It is roughly right — and it is the only band it is roughly right for.
Between 7 and 27 minutes, depending on the month.
You are the default, which is its own problem
Almost every public recommendation quietly assumes this band. That makes the familiar figure usable for you, but it also means you inherit a number that was never qualified, and the qualification matters more than the figure. Season moves it further than anything except skin: the same body at the same latitude needs a small fraction of the time at midsummer that it needs at the edge of the season, and below a certain sun angle no length of exposure works at all. The number you have been given is a midsummer number wearing no label.
Fitzpatrick III and IV: skin that sometimes burns and tans gradually, or rarely burns and tans easily.
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: 18–35 min
- March: 12–27 min
- April: 9–17 min
- May: 8–13 min
- June: 7–12 min
- July: 7–11 min
- August: 8–14 min
- September: 9–19 min
- October: 13–34 min
- November: 23–36 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 7 min, against roughly 31 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
Several times longer, and the season closes earlier than the calendar suggests.
Type 5–6: 19–72 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.