Caffeine Half-Life Calculator

How to use

1. Pick a drink from the dropdown, or choose Custom and enter a mg amount.
2. Set how many hours ago you had it (0 = right now).
3. Adjust the half-life if you have a reason to (5 h is the population average).
4. The chart and table show what's left now and at +1 / +3 / +6 / +12 / +24 hours.

Frequently asked questions

Where does the 5-hour half-life come from?

Pharmacokinetic studies put healthy-adult caffeine half-life in the 3–7 hour range, averaging around 5. Pregnancy roughly doubles it (up to 10–15 h in the third trimester); smoking shortens it by ~30–50 %; oral contraceptives lengthen it.

What is the 100 mg sleep threshold?

A rough cut-off — research generally finds caffeine within 6 hours of bedtime can delay sleep onset and reduce sleep efficiency. 100 mg is the level at which most people stop noticing an effect. Your own tolerance varies.

Are the drink amounts accurate?

They're typical values — a single espresso averages ~63 mg, an 8-oz brewed cup ~95 mg. Individual brews vary a lot (cold brew can be higher; decaf is ~3 mg). Use the Custom field if you have a precise number from a label.

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