Insect Repellent Calculator
Protection hours and reapplies from DEET percent.
What it does
DEET percent is a clock, not a shield rating: stronger juice lasts longer against mosquitoes and ticks without hitting harder. Picking the band to match the outing beats maxing percent for a short walk.
The tool above takes DEET percent with hours outdoors. It returns protection per coat with the coat count, so reapply timing lands before bites restart.
The defaults (25% DEET, 8 h out) protect about 5 h a coat and take 2 coats with 1 reapply. Light 8% juice for 6 h protects about 2 h a coat and takes 3 coats instead.
Bands follow EPA DEET registration review with CDC Yellow Book matching: under 10% runs about 1 to 2 hours, higher runs longer, efficacy flattens near 50%, and labels rule over math. EPA lists 5 to 99% products spanning roughly 2 to 12 mosquito hours.
How to use
- Read DEET percent off the label.
- Enter hours outdoors.
- Read protection per coat.
- Read total coats needed.
- Set reapply by the clock, not bites.
- Follow label frequency caps always.
Formula
- %
- DEET concentration on the label.
- band
- Conservative protection hours per coat.
- ceil
- Round up: any part hour needs a full coat.
Bands run conservative against EPA ranges because sweat, water, and rubbing shorten real wear. Above 50% the CDC notes little extra time, so this page caps at 6 h and says so rather than promising the full 12.
Worked example
Example: 25% DEET, 8 hours out
Defaults: 25% concentration, 8 h outdoors.
- Band: 25 sits 20 to 30, so 5 h.
- Coats: 8 / 5 = 1.6, round up to 2.
- Reapplies: 2 - 1 = 1 reapply.
- Tool shows about 5 h, 2 applications, 1 reapply.
- Light check: 8% for 6 h gives 2 h bands, 3 coats.
- Label frequency caps beat this math when they differ.
Reference table
| Label | Per coat | Fits |
|---|---|---|
| Under 10% | 2 h | Short walks |
| 10 to 20% | 3 h | Half days |
| 20 to 30% | 5 h | Full days |
| Over 30% | 6 h capped | Long exposure |
Limits
- Bands are conservative, not label promises.
- Sweat, swim, and rub shorten wear.
- Ticks and mosquitoes read separately.
- Kids, pregnancy, and gear need label checks.
Common mistakes
- Buying max percent for a short walk.
- Reapplying by bites instead of clock.
- Layering under clothing per label bans.
- Skipping sunscreen first ordering.
- Exceeding label frequency after swims.
Try it yourself
Quick checks. Answers sit tucked under each question.
8% for 6 h gives what?
About 2 h a coat, 3 applications, 2 reapplies.
35% for 5 h gives what?
About 6 h a coat, 1 application, no reapply.
Why cap over 30%?
CDC notes little extra past 50%; labels rule the top end.
Questions
How long does DEET last?
Roughly 2 h under 10% to 5 plus h at 20 to 30%, label rules.
Stronger DEET better?
Longer, not stronger; past 50% adds little time.
Sunscreen plus repellent?
Sunscreen first, repellent over it, per CDC ordering.
Kids safe?
EPA sets no age bar for DEET but labels rule; keep off hands, eyes, and cuts.
Tick vs mosquito hours?
EPA spans 2 to 10 h ticks with 2 to 12 h mosquitoes by percent.
What beats spray alone?
Treated clothing, covered skin, and dumping standing water.