Daily Sunlight Exposure for Vitamin D Calculator
Enter your location, skin tone, and season to calculate optimal sunlight exposure for vitamin D synthesis.
0°=Equator, 23°=Tropic, 40°=NY/Spain, 60°=Alaska/Scandinavia
Face/hands ~5%, Arms+Legs ~25%, Swimsuit ~40%, Nude ~100%
Vitamin D synthesis drops 50% by age 70
How much sunlight do I need for adequate vitamin D?
Depends on: Skin tone (lighter = faster), Time of day (10am-2pm best), Season (winter needs 2-3x longer), Latitude (above 37° struggles Nov-Feb). Fair skin: 10-15 min midday summer. Medium: 15-30 min. Dark: 30-60 min. Winter: 2-3x longer or supplement 2,000-5,000 IU/day.
Can you get vitamin D through a window?
No! Glass blocks UVB rays (which create vitamin D) while letting UVA through (causes aging). You need direct sunlight exposure. Car windows, office windows, sunglasses with UV protection all prevent vitamin D synthesis. Glass blocks 95-99% of UVB rays.
What SPF blocks vitamin D production?
SPF 15 blocks 93% of UVB (vitamin D production). SPF 30 blocks 97%. SPF 50 blocks 98%. Even SPF 8 blocks 95%. Solution: Expose arms/legs for 10-15 min before applying sunscreen, or use "sunsafe" time (before 10am, after 4pm) for longer exposure without burning.
Which body parts produce the most vitamin D?
Largest surface area = most production. Best: Back (highest), Chest, Abdomen, Thighs. Moderate: Arms, Shoulders. Poor: Face, Hands (only 5-10% of production). Expose 25-40% of body for optimal synthesis. Swimsuit = 100% exposed surface vs. face/hands only = 5% (requires 20x longer).