Vitamin D from Sun Exposure Calculator
Estimate IU of Vitamin D your body produces from sunlight.
Frequently Asked Questions — Vitamin D Calculator
How does the body make Vitamin D from sun?+
UVB rays (280-315nm) from sunlight penetrate the skin and convert 7-dehydrocholesterol to previtamin D3, which becomes D3. The process requires UV index ≥3 and exposed skin (face, arms — not through glass or sunscreen SPF 15+).
Does SPF sunscreen block Vitamin D production?+
SPF 30 blocks ~97% of UVB, significantly reducing Vitamin D synthesis. However, in practice, most people don't apply sunscreen perfectly (or to all areas), so some synthesis still occurs. A reasonable approach: 10-15 min unprotected sun, then apply SPF.
Can you get Vitamin D deficiency in summer?+
Yes — if you work indoors all day, cover all skin, use SPF consistently, or have very dark skin at high latitudes. Also: getting sun through windows doesn't work (glass blocks UVB). Check serum 25(OH)D levels to confirm.