Home · Caffeine half-life
Caffeine calculatorHow much caffeine is left at bedtime?
Caffeine has a ~5-hour half-life. Enter your drink, when you had it and your bedtime to see how much is still keeping you awake.
Using a typical 5-hour half-life.
≈ 8 h after your drink · about 1.6 half-lives elapsed.
Under ~50 mg at bedtime is unlikely to disturb most sleepers. Want to know how much you can have in the first place? Use the daily intake calculator.
Estimates use a single-compartment half-life model. Real clearance depends on genetics, medication, pregnancy and liver function — treat results as a guide.
How long caffeine really lasts
Caffeine is cleared on a curve, not a cliff. With a typical 5-hour half-life, half the dose is gone every 5 hours:
- 0 h: 100% — full dose
- 5 h: 50% remaining
- 10 h: 25% remaining
- 15 h: ~12% remaining
That's why an afternoon coffee can still affect sleep at night. Research has found caffeine taken even 6 hours before bed can cut total sleep time and reduce deep sleep — often without you noticing, because you still fall asleep.
Slow metabolisers — including many pregnant people and anyone on certain medications — can have a half-life of 8 hours or more, doubling how long caffeine lingers.
Sleep better after a late coffee
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Frequently asked questions
How long does caffeine stay in your system?
With a ~5-hour half-life, a 200 mg coffee leaves about 100 mg at 5 hours, 50 mg at 10 hours and 25 mg at 15 hours. It's rarely fully gone before the next morning.
When should I stop drinking coffee before bed?
A safe rule is at least 8 hours before bed. The cutoff card above shows the latest time you could have your drink and still be under ~25 mg at bedtime.
Why can I fall asleep after coffee but still sleep badly?
Caffeine blocks the “tired” signal but doesn't switch it off — even when you fall asleep, lingering caffeine reduces deep, restorative sleep, so you wake less refreshed.