Sunscreen SPF Protection Time Calculator
Calculate sunscreen time from SPF, Fitzpatrick skin type (I-VI), and UV index.
Returns exposure window and reapplication schedule for outdoor activities.
How SPF Works SPF (Sun Protection Factor) indicates how much longer you can stay in the sun without burning compared to wearing no sunscreen.
The simplified formula: Protected Time = Base Burn Time × SPF × Real-World Factor
The real-world factor accounts for the fact that most people apply about one-third of the tested amount, which dramatically reduces effective protection.
Base Burn Times by Fitzpatrick Skin Type Type 1, Very Fair (always burns, never tans): ~10 minutes Type 2, Fair (usually burns, sometimes tans): ~15 minutes Type 3, Medium (sometimes burns, gradually tans): ~20 minutes Type 4, Olive (rarely burns, always tans): ~30 minutes Type 5, Brown (very rarely burns, tans deeply): ~45 minutes Type 6, Dark (never burns, deeply pigmented): ~60 minutes
UV Index Impact The UV Index (1-11+) measures the intensity of UV radiation. Higher UV Index means sunburn happens faster. UV 1-2: Low risk, SPF 15 sufficient UV 3-5: Moderate, SPF 30 recommended UV 6-7: High, SPF 30-50 essential UV 8-10: Very High, SPF 50 and protective clothing UV 11+: Extreme, minimize exposure entirely
What SPF Blocks SPF 15 blocks 93.3% of UVB rays SPF 30 blocks 96.7% of UVB rays SPF 50 blocks 98.0% of UVB rays SPF 100 blocks 99.0% of UVB rays
Higher SPF gives diminishing returns. There is no SPF that blocks 100%.
Always Reapply No matter how high your SPF, reapply every 2 hours and immediately after swimming or sweating. Water-resistant formulas maintain efficacy for 40 or 80 minutes in water.