How much sun do you actually need?
Enough sunlight to make vitamin D, not so much that you burn. The gap between those two is narrower than most people think, and in winter at high latitudes it closes completely: the sun never climbs high enough to make any vitamin D at all, however long you stay out.
Find your city
1,000 cities, each with its own vitamin D winter dates, exposure times by skin type, and the hours of the day that actually work.
What this calculates
- Minutes to 1000 IU — for your skin type and how much skin you have exposed.
- Minutes to sunburn — the ceiling on the same exposure.
- Percentage of your daily requirement — from a fixed 15 minutes.
The solar geometry is exact. The atmospheric part is a clear-sky model, so every figure is an upper bound — real cloud, shade and sunscreen all reduce it. The methodology page sets out the sources, the assumptions and the known limitations in full.