Sunscreen SPF Calculator

What SPF should I use daily?

Dermatologists recommend SPF 30 as the minimum for daily outdoor use, and SPF 50 for beach, skiing, or high-altitude activities. SPF 15 is only adequate for brief incidental exposure (walking to your car). Note: SPF 30 blocks 97% of UVB; SPF 50 blocks 98% — the difference is small, but SPF 50 provides a meaningful buffer when you inevitably apply less than the recommended amount.

What is the Fitzpatrick skin type scale?

The Fitzpatrick scale classifies skin into 6 types based on reaction to UV exposure: Type I (very fair, always burns, never tans) through Type VI (dark, never burns). It was developed by Harvard dermatologist Thomas Fitzpatrick in 1975 and is still used by dermatologists and sunscreen researchers to assess sun sensitivity.

How often should I reapply sunscreen?

Reapply every 2 hours of outdoor exposure, or immediately after swimming, sweating heavily, or towel-drying. No sunscreen lasts all day — even "all-day" or "sport" formulas need reapplication. Water-resistant sunscreens maintain protection for 40–80 minutes in water, not indefinitely.

Does sunscreen prevent vitamin D production?

In theory, SPF 30 could reduce vitamin D synthesis by 95%. In practice, most people don't apply enough sunscreen to achieve labeled SPF, and they expose skin outside the protected area (like arms or legs not covered). Most people with sun-protective habits still produce adequate vitamin D. If concerned, get vitamin D levels tested and supplement if necessary — don't skip sun protection.