Sunscreen Calculator

Calculate sun protection time based on skin type, UV index, and SPF. Get reapplication schedule.

By Konstantin Iakovlev · Updated April 2026 · Source: CDC

Skin Type (Fitzpatrick)
hours

Time to Burn (No SPF)

17 min

Theoretical Protection

500 min

Effective Protection

120 min

Reapplications Needed

1

Reapplication Schedule

Reapply 12h after first application

Fitzpatrick Skin Types

Type IVery fair, always burns
Type IIFair, burns easily
Type IIIMedium, sometimes burns
Type IVOlive, rarely burns
Type VBrown, very rarely burns
Type VIDark, never burns

Vitamin D Note

While sun protection is important, your body needs some UV exposure for vitamin D production. Most people get sufficient vitamin D with brief, incidental sun exposure. Consider a supplement if you have limited outdoor time.

Always reapply sunscreen every 2 hours and after swimming or sweating, regardless of SPF. No sunscreen blocks 100% of UV rays. Seek shade during peak hours (10 AM – 4 PM).

Use the Sunscreen Calculator above to calculate your results. Enter your values and see instant results — all calculations run in your browser.

Disclaimer: This calculator is for informational purposes only and does not constitute tax, financial, or legal advice. Results are estimates based on the information you provide and current rates. Always consult a qualified tax professional or financial advisor for advice specific to your situation.

How It Works

How long you can stay outdoors before your skin starts to burn depends on three things working together: your skin type, the strength of the sun at that moment, and the product you put on. Pairing those variables gives you a reapplication window rather than a guess, which matters for avoiding sunburn and lowering long-term skin cancer risk. With UV levels expected to stay high through 2026, knowing your own safe window helps you plan exposure instead of reacting to redness after the fact.

The estimate starts from your skin's natural burn time, known as the Minimal Erythemal Dose (MED), which is read from your Fitzpatrick skin type. That baseline is multiplied by the SPF factor of your sunscreen to find your total protected time, then adjusted for the current UV index, since stronger solar radiation shortens how long any given protection lasts. Finally, roughly 20% is shaved off the result to account for sweating, towel drying, and other everyday losses, keeping the figure deliberately conservative.

No product blocks 100% of UV, so the number you get is a ceiling, not a promise. Reapply after swimming or heavy sweating, and cover the spots people routinely skip, such as the ears, the back of the neck, and the tops of the feet. Going above SPF 50 buys very little extra time, so careful, even application and timely reapplication do far more for your skin than chasing an ultra-high number on the bottle.

Example: A Day at the Beach in July 2026

  1. 1 Sarah, with Fitzpatrick Skin Type II (burns easily, tans minimally), is planning a beach day in July 2026 where the UV Index is predicted to be 9. She's using an SPF 30 broad-spectrum sunscreen.
  2. 2 Her natural burn time for Skin Type II at UV Index 9 is estimated at 15 minutes. With SPF 30, her theoretical protection is 15 minutes * 30 = 450 minutes. After accounting for real-world factors and reapplication recommendations, her effective protection time is calculated.
  3. 3 Sarah's estimated sun protection time before needing reapplication is approximately 3 hours and 30 minutes.
  4. 4 To maintain optimal protection, Sarah should plan to reapply her SPF 30 sunscreen every 3 hours and 30 minutes, or sooner if she's swimming or sweating heavily. Additionally, seeking shade during peak UV hours (10 AM - 4 PM) and wearing protective clothing are highly recommended for comprehensive sun safety.

Source: CDC · Last updated: April 2026

Frequently Asked Questions

How long does SPF 30 protect me?
SPF 30 blocks about 97% of UVB rays. If you would burn in 10 minutes without sunscreen, SPF 30 theoretically extends that to 300 minutes. However, dermatologists recommend reapplying every 2 hours regardless of SPF, and after swimming or sweating.
Is SPF 50 much better than SPF 30?
The difference is small: SPF 30 blocks 97% of UVB rays, SPF 50 blocks 98%. No sunscreen blocks 100%. The bigger factor is proper application (1 oz for full body) and reapplication every 2 hours. SPF 30 with proper application outperforms SPF 100 applied thinly.
How much sunscreen should I apply?
Use approximately 1 ounce (a shot glass full) for your entire body and a nickel-sized amount for your face. Most people apply only 25-50% of the recommended amount, which dramatically reduces protection. A family of four should go through a bottle per day at the beach.

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