Vitamin D Calculator
How much sun does your skin need to make vitamin D — without burning? Set your skin type, the UV index and how much skin is exposed for a rough, conservative estimate.
Check the live UV index. Below UV 3, little to no vitamin D is made.
This is an estimate, not medical advice. The figure is deliberately well below your burn time — never let vitamin D be a reason to stay out until you redden. If you’re worried about deficiency, ask your doctor for a blood test.
How the estimate works
Vitamin D is made when UVB reaches bare skin. Research suggests roughly a quarter of the dose that would redden your skin (a “sub-erythemal” dose), over a decent area, is enough to top up vitamin D. So this tool takes your personal burn time, takes about a quarter of it, and adjusts for how much skin is exposed.
- Skin type — more melanin (higher type) slows synthesis, so it needs longer.
- UV index — more UVB means faster synthesis; under UV 3 it barely happens.
- Exposed area — more skin in the sun means less time needed.
Want the detail? Read getting vitamin D from sunlight, and check how long before you’d burn with the Tanning Time Calculator.
Frequently asked questions
How much sun do I need for vitamin D?
For fair skin, often just 10–20 minutes of midday sun on bare arms and legs a few times a week is enough in summer. Darker skin needs noticeably longer because melanin slows vitamin D production. The estimate above tailors this to your skin type and the UV index.
Can I make vitamin D in winter or early morning?
Usually very little. Vitamin D needs UVB, which mostly arrives when the UV index is 3 or higher — around the middle of the day in spring, summer and autumn. In winter at high latitudes the sun is too low, so diet or supplements are the reliable route.
Does sunscreen stop vitamin D?
In theory high SPF reduces UVB and therefore vitamin D synthesis, but in real-world use people apply too little for it to block much. Don’t skip sunscreen to chase vitamin D — get brief unprotected exposure well within your burn time, or supplement.
Is this medical advice?
No. This is an educational estimate based on published UV models. Vitamin D needs vary with age, weight, health and location. If you think you’re deficient, ask your doctor for a blood test rather than relying on sun exposure.
Your tan, planned by the hour.
Everything on this site, plus live UV by the hour, a burn-timer that counts down for your skin, SPF reapply reminders and push alerts the moment your safe window opens.