Estimate how long you can stay in the sun with sunscreen: your skin type sets your unprotected burn time, the UV index scales it, and SPF multiplies it.
Result
How to use this tool
Pick the Fitzpatrick skin type closest to yours.
Enter the current UV index (weather apps and forecasts publish it).
Enter the SPF printed on your sunscreen.
Read the estimated protected time, and still reapply every 2 hours.
Formula & worked example
Type II skin burns in about 20 minutes at UV index 5; with SPF 30 that stretches to about 600 minutes, but reapplication every 2 hours still applies.
Limitations — read this before you rely on it
Skin-type minutes are typical values, not personal measurements; real burn time varies with altitude, cloud, reflection, clothing, sweating and application thickness. This estimates reddening time, not safety from long-term UV damage. This tool is for education only and is not medical advice. Talk to a clinician about any result that worries you, and never change treatment because of a calculator result.
Frequently asked questions
SPF 30 means skin takes roughly 30 times longer to redden than without sunscreen, assuming a full 2 mg/cm² application. In practice most people apply less and get less.
The UV index measures burning UV strength. Doubling it roughly halves the time to burn, which is why midday summer sun is far harsher than morning sun.
Not much: SPF 30 blocks about 97% of UVB, SPF 50 about 98% and SPF 100 about 99%, assuming correct application. Technique matters more than the number.
No. Sunscreen rubs and sweats off, and no sunscreen blocks all UV. Reapply every 2 hours and seek shade in the middle of the day.
SPF only rates UVB. Choose a broad-spectrum product for UVA protection too, since UVA drives ageing and contributes to skin cancer risk.