Health · SPF reality check
Sunscreen SPF Reality Check
Enter your SPF, skin type, hours in the sun, reapplication, and coverage to find out how much of your sun exposure was actually protected.
Instant result
Plain-English why
Copyable takeaway
What this means
This tool estimates effective sun protection by combining SPF, skin type, coverage quality, and reapplication — then comparing it to actual sun exposure.
Formula used
Effective protection (minutes) = skin baseline burn time × SPF value × coverage factor × reapplication factor. Compared to actual sun exposure time.
Worked example
Fair skin (10 min baseline), SPF 50 (×50), thorough coverage (×1.0), no reapplication (×0.4): effective cover = 200 minutes. 5 hours in sun = 300 minutes. Protection ran out — gaps in the afternoon.
Common questions
Why does reapplication matter so much?
SPF protection degrades with sweat, contact, and time. Most sunscreens offer their stated protection for about 2 hours under active conditions. Without reapplication, effective protection drops significantly — the coverage penalty in this tool reflects the well-documented real-world reduction in effectiveness from single application.
Does higher SPF mean proportionally more protection?
Not linearly. SPF 15 blocks about 93% of UVB. SPF 30 blocks about 97%. SPF 50 blocks about 98%. The jump from 15 to 30 is meaningful; from 30 to 50 less so. Application amount and reapplication frequency matter more than SPF level above 30.
Plain-English summary
Enter your sunscreen details and sun exposure to find out how much of your time in the sun was actually protected.
This section translates the result into a short, direct takeaway rather than leaving the page at a bare number.
Read the guide
How SPF actually works — and why most people are using it wrong
The SPF number tells you less than you think. Coverage and reapplication matter more. Here's what the number actually means in practice.
Read the guideRelated instruments
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