How long in the sun
How long in the sun do you need for vitamin D?
There is a number everyone repeats, and it is wrong for most people.
Between 5 and 30 minutes, for the same latitude, the same hour and the same amount of skin uncovered. The only thing that changes is the skin.
Why the usual answer misses
"Ten to fifteen minutes" is the figure that circulates, and it is a real measurement — of one kind of skin. Melanin absorbs the same ultraviolet that makes the vitamin, so the darkest skin needs about six times as long as the lightest for the identical dose. Ten minutes is close to right in the middle of the range and wrong at both ends: too long for very fair skin, less than half of what the darkest skin needs. A search engine cannot fix this, because the answer depends on who is asking.
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.
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
Find your range
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
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.