☀️ SPF Calculator
Choose your skin type, your sunscreen's SPF, and today's UV index to see how long you're protected from burning — and when to reapply.
🧴 Estimate Your Sun Protection Time
What is an SPF Calculator?
It estimates how long sunscreen keeps your skin from burning. Pick the Fitzpatrick skin type that matches how quickly you burn, enter the SPF you're wearing and the UV index for today, and it multiplies your baseline burn time by the SPF, then adjusts for how strong the sun is right now.
Use it to plan a day at the beach, a hike, or poolside lounging — and to remind yourself when it's time to reapply. Sweat, swimming, and towel-drying all cut real protection short, so dermatologists recommend reapplying at least every two hours no matter what the math says.
❓ Frequently Asked Questions
How does the SPF calculator work?
Pick the skin type that best matches how quickly you burn, enter the SPF of the sunscreen you're wearing, and today's UV index. The calculator multiplies your skin's unprotected burn time by the SPF, then divides by the UV index to estimate how many minutes of protection you have — plus a reminder to reapply at least every two hours.
Does a higher SPF mean I can stay in the sun longer without reapplying?
In theory, yes — SPF 50 protects roughly twice as long as SPF 25 under the same conditions. In practice, sweat, water, swimming, toweling off, and simply not applying enough sunscreen all shorten real protection, so dermatologists recommend reapplying at least every two hours regardless of SPF.
Why does UV index change my protection time so much?
UV index measures the strength of the sun's ultraviolet radiation at a given time and place. A higher UV index delivers burning radiation faster, so the same skin and SPF combination protects for a shorter stretch of time on a UV index 10 day than on a UV index 3 day.
What is a Fitzpatrick skin type?
It's a classification (Type I to Type VI) describing how skin responds to UV exposure, from very fair skin that always burns and rarely tans (Type I) to deeply pigmented skin that almost never burns (Type VI). It's a useful shorthand for baseline burn time, but everyone should still wear sunscreen and watch for signs of overexposure.