Caffeine Half-Life Calculator — How Long Until It Wears Off?
Estimate remaining caffeine after your last cup and see when it drops toward half, a quarter, or nearly gone.
What this tool does
“How long does caffeine last?” is really a pharmacokinetics question dressed as a lifestyle worry. Caffeine’s average half-life in healthy adults is about 5–6 hours, so a 2 pm cold brew can still be meaningful at 10 pm. This calculator estimates remaining milligrams over time so you can plan the last cup before bed — not diagnose metabolism.
Many adults land near 5–6 hours. Pregnancy, genetics, and some medications change this.
Estimated caffeine still in your system
65 mg
of 95 mg starting dose (69% left)
Until ~50% left
2.5 h
Until ~25% left
8 h
Until ~10% left
15.3 h
| Hours from now | Approx left |
|---|---|
| +0 h | 65 mg |
| +1 h | 57 mg |
| +2 h | 51 mg |
| +3 h | 45 mg |
| +4 h | 39 mg |
| +5 h | 35 mg |
| +6 h | 31 mg |
| +8 h | 24 mg |
| +10 h | 18 mg |
| +12 h | 14 mg |
Educational estimate only — not a medical test. Feelings of alertness do not always match blood caffeine.
Rough remaining caffeine (5.5 h half-life)
Starting from a 190 mg large drip at hour 0.
| Hours later | Approx left | % of dose |
|---|---|---|
| 0 h | 190 mg | 100% |
| 3 h | 132 mg | ~70% |
| 5.5 h | 95 mg | 50% |
| 8 h | 70 mg | ~37% |
| 11 h | 48 mg | 25% |
Why afternoon coffee ruins sleep for some people
If your half-life is on the long side, a 3 pm cup still leaves a large fraction of caffeine at 11 pm. You may not feel “wired,” but deep sleep can still suffer. Earlier cutoffs beat sleep aids stacked on late espresso.
Coffee and anxiety timing
Caffeine’s stimulant window overlaps with anxious body signals (faster heart rate, restlessness). Spacing doses and avoiding huge late boluses helps many people keep coffee without the panic-adjacent feeling — see our coffee and anxiety guide for more context.
How to use this tool
Choose a dose
Pick a common coffee drink or enter a custom milligram amount if you know your brand’s caffeine number.
Set how long ago you drank it
The readout shows estimated caffeine still circulating right now, plus a timeline of the next several hours.
Adjust half-life if you know you are sensitive
Slow metabolizers and pregnancy often mean a longer half-life; some people clear caffeine faster. Move the slider to explore, then use sleep quality as the real feedback loop.
Plan your cutoff
Look at when the dose falls toward 25% or 10% relative to bedtime. If you still feel wired, pull the last cup earlier tomorrow — calculators approximate; your nights are the truth.
Pro tips
- Half-life is not the same as “I feel normal.” Subjective alertness fades before caffeine fully clears.
- Stacking drinks resets the clock — two coffees four hours apart leave more in your system than one morning cup.
- Energy drinks plus coffee is a common way people accidentally double dose for evening events.
- Pair this tool with the daily caffeine calculator to stay under ~400 mg while also protecting sleep timing.
Why it matters
Sleep disruption is one of the biggest real-world downsides of coffee. A half-life tool targets high-intent queries (“how long does coffee stay in your system,” “when does caffeine wear off”) and supports the health content cluster around anxiety, empty-stomach coffee, and daily limits.
Frequently asked questions
What is the half-life of caffeine?
For many healthy adults, caffeine’s half-life is about 5–6 hours — meaning roughly half the dose is still in your system after that time. Genetics, pregnancy, liver health, and some medications can shorten or lengthen it.
How long does caffeine last?
You may feel peak effects within an hour, but meaningful amounts can remain for 8–12+ hours after a large dose. That is why afternoon coffee wrecks sleep for many people.
How long does coffee stay in your system?
Coffee’s caffeine clears gradually. After one half-life (~5–6 hours) about half remains; after two half-lives about a quarter remains. Trace amounts linger longer.
When should I stop drinking coffee to sleep?
A common rule is 8+ hours before bed. If you are sensitive, stop by early afternoon. Use the calculator with your real dose and bedtime to see what is still circulating.
Does food change caffeine half-life?
Food can slow absorption slightly so the “hit” feels smoother, but it does not dramatically change the overall half-life for most people.