Sunscreen Schedule Calculator
Reapply count, exact times, and swim reminder from start and end times.
What it does
Sunscreen protection fades on a clock: about every two hours outdoors, plus immediately after swimming or heavy sweating. A full beach day from 10 to 4 needs four timed applications, not one morning coat.
The tool above takes first application with last outdoor time. It returns the application count with exact times and a swim reminder beside them.
The default of 10:00 to 16:00 gives 4 applications at 10:00, 12:00, 14:00, and 16:00. A 9:00 to 13:00 morning gives 3 at 9:00, 11:00, and 13:00.
The timing follows dermatology academy sunscreen guidance with application guides matching each rule. Both set SPF 30+ broad-spectrum with two hour reapplication, sooner with water or sweat.
How to use
- Enter the first application time.
- Enter when outdoor time ends.
- Say whether swimming or sweating happens.
- Read the times and set phone alarms.
- Reapply right after water regardless.
Formula
- 2 h
- Reapplication interval outdoors.
- SPF 30+
- Blocks 97% of UVB when applied generously.
- swim
- Water or sweat: reapply at once.
Sunscreen math assumes generous coats: most people apply half enough, halving real protection. Face alone wants a full teaspoon per coat.
Worked example
Example: 10:00 to 16:00
Defaults: start 10:00, end 16:00, no swim.
- Interval: every 2 hours from 10:00.
- Times: 10:00, 12:00, 14:00, 16:00.
- Count: 4 applications.
- Swim rule: none today, so the clock stands.
- Tool shows 4 applications with the four times.
Reference table
| Hours out | Applications | Times |
|---|---|---|
| 10:00-16:00 | 4 applications | 10:00, 12:00, 14:00, 16:00 |
| 9:00-13:00 | 3 applications | 9:00, 11:00, 13:00 |
| 12:00-18:00 | 4 applications | 12:00, 14:00, 16:00, 18:00 |
Limits
- Timing aid only, not medical advice.
- SPF 30+ broad-spectrum assumed throughout.
- Shade, hats, and sleeves beat lotion alone.
- Babies under 6 months need shade, not sunscreen.
Common mistakes
- One morning coat for the whole day.
- Skipping reapply after swimming.
- Thin coats that halve real SPF.
- Expired bottles with faded filters.
- Forgetting ears, neck, feet, and scalp part.
Try it yourself
Quick checks. Answers sit tucked under each question.
9:00 to 13:00?
3 applications: 9:00, 11:00, 13:00.
Swimming at noon?
Reapply right after: water restarts the clock.
End before start?
Rejected: end must sit after start on the same day.
Questions
How often reapply sunscreen?
About every 2 hours outdoors, and right after swimming or sweating.
What SPF?
30 or higher, broad-spectrum, water resistant.
Cloudy days too?
Yes. Up to 80% of UV passes clouds.
How much per coat?
Generously: a shot glass for the body, a teaspoon for the face.
Higher SPF lasts longer?
No. High numbers block slightly more, never longer.
Babies and sunscreen?
Shade first under 6 months; 6+ months get SPF 30+ per label.