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Caffeine Half-Life Calculator
Caffeine leaves your body slowly — about half is gone every five hours. See how much of your last coffee is still with you at bedtime.
Free · no signup · updated August 2026
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The half-life arithmetic
Caffeine is cleared exponentially with an average half-life of about 5 hours in healthy adults: after 5 hours half of the dose remains, after 10 hours a quarter, after 15 hours an eighth. Individual clearance ranges roughly 3–7 hours — slower with some medications and in pregnancy, faster in regular smokers — so treat this as a well-grounded estimate, not a lab result.
| Drink | Typical caffeine |
|---|---|
| Filter coffee, mug | 90–140 mg |
| Espresso, single shot | 60–80 mg |
| Black tea, cup | 40–50 mg |
| Green tea, cup | 25–35 mg |
| Cola, 330 ml can | 30–40 mg |
| Energy drink, 250–500 ml | 80–160 mg |
The sleep-relevant threshold used here is ~100 mg at bedtime: a controlled trial found 400 mg taken even 6 hours before bed still cut measured sleep by over an hour. The practical rule that falls out of the maths: keep big doses to the morning, and make the afternoon coffee the small one.
Frequently asked questions
How long does caffeine stay in your system?
Caffeine's average half-life is about 5 hours in healthy adults (individual range roughly 3–7). After 5 hours half remains; after 10 hours a quarter. A 200 mg mug at 15:00 still leaves ~65 mg at 23:00 — enough to measurably affect sleep in sensitive people.
How much caffeine is in coffee, tea and cola?
Typical figures: filter coffee 90–140 mg per mug, espresso 60–80 mg per shot, black tea 40–50 mg, green tea 25–35 mg, cola 30–40 mg per can, energy drinks 80–160 mg per can. Strength varies a lot between brands and brews.
When should I stop drinking coffee before bed?
A common evidence-based rule is to stop 8+ hours before bedtime; one well-known trial found 400 mg taken even 6 hours before bed still disrupted measured sleep. This tool shows your personal cutoff for staying under ~100 mg at lights-out.
Is caffeine bad for me?
Up to about 400 mg a day is considered safe for most healthy adults (pregnancy guidance is lower — commonly 200 mg). The issue this calculator addresses is timing: caffeine late in the day trades tomorrow's energy for tonight's sleep.
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Estimates for general information only, not medical advice. BMR/TDEE use the Mifflin-St Jeor equation; individual needs vary.
