How long does caffeine stay in your system?
Caffeine in your system
Projected: one filter coffee at 18:22. Add what you've actually had to replace it.
Cycle-aligned wake-up times
Counting forward from your bedtime in 90-minute cycles. Waking at the end of a cycle tends to feel easier than waking mid-cycle. These are windows, not appointments — real cycles run 70 to 120 minutes and vary night to night.
- 04:55–05:35 4 cycles · 6 h of sleep
- 06:20–07:10 5 cycles · 7 h 30 min of sleep
- 07:45–08:45 6 cycles · 9 h of sleep
Add what you drank and when. The curve shows how much is left at any point tonight.
Half of this cup is still with you in five hours. A quarter of it in ten.
What half-life means here
Half-life is the time it takes for half of a dose to be eliminated. Caffeine averages about 5 hours in healthy adults, with a normal range of roughly 3 to 7. It is not a countdown to zero: each half-life removes half of whatever is left, so the curve falls fast at first and then trails.
A 95 mg coffee at 08:00, on a 5-hour half-life, is down to 47.5 mg by 13:00, 23.8 mg by 18:00 and about 11.9 mg by 23:00. It never quite reaches nothing, which is why this tool talks about being under a level rather than being clear.
What changes your half-life
Caffeine is broken down mostly by one liver enzyme, CYP1A2, and anything that speeds up or slows down that enzyme moves your half-life with it.
Nicotine induces CYP1A2 and roughly halves caffeine half-life, which is why smokers often drink more coffee for the same effect — and why quitting can make the same coffee suddenly feel like too much. Hormonal contraceptives inhibit it and roughly double it. Pregnancy slows clearance progressively, from around 1.6× in the first trimester to 3× or more in the third, where half-life can reach 15 hours.
Liver impairment and some medications — fluvoxamine is the strongest example — change it far more than any of these. This tool does not model them. If either applies to you, a clinician is a better source than a calculator.
Absorption, and what this model simplifies
This tool treats a drink as arriving in your bloodstream instantly. In reality caffeine peaks 30 to 60 minutes after you drink it, though oral bioavailability is close to 100%, so the total that arrives is nearly the whole dose.
Over the four to ten hour horizons the calculator works across, that simplification barely matters. It does make the first hour of the curve slightly wrong — it shows the peak immediately rather than climbing to it — and it is worth knowing that before reading anything into the first segment.
A worked example
A 400 mg dose — about four filter coffees, or one large pre-workout — taken 6 hours before bed, on an average 5-hour half-life.
Six hours is 1.2 half-lives, so 400 × 0.5^1.2 leaves 174 mg on board at bedtime. That is the dose and timing used in the Drake study, where it cost participants about an hour of sleep.
Change nothing but the metabolism. On a 4-hour half-life the same dose leaves 141 mg; on a 7-hour half-life it leaves 221 mg. The drink and the timing were identical.
Common questions
How long does it take for caffeine to fully wear off?
Never completely. Caffeine decays exponentially, so it approaches zero without reaching it. Practically, about 3% is left after five half-lives — roughly 25 hours on an average 5-hour half-life. Half is gone after 5 hours and a quarter after 10.
What is the 2 hour coffee rule?
There is no single accepted version — the phrase gets attached to waiting two hours after waking before the first cup, and to leaving two hours between coffee and an iron supplement or thyroid medication. None of them is about sleep. For the sleep question the arithmetic is unambiguous: two hours is well under one half-life, so a 95 mg coffee still leaves 72.0 mg.
Why does caffeine affect some people more than others?
Mostly CYP1A2 activity, which varies genetically and is pushed around by nicotine, hormonal contraceptives and pregnancy. Two people drinking the same coffee can be left with very different amounts six hours later.
Does caffeine half-life change with age?
Not dramatically in healthy adults. It is markedly longer in newborns, and liver function matters more than age itself in older adults.
Do smokers clear caffeine faster?
Yes — nicotine induces CYP1A2 and roughly halves caffeine half-life. This is also why caffeine intake often needs revisiting after quitting.
How long does caffeine last in pregnancy?
Clearance slows considerably and progressively, reaching 15 hours or more in the third trimester. Clinical guidance on caffeine limits during pregnancy is more useful than any calculator estimate.
What this cannot tell you
- Your own half-life. The 3-to-7-hour range for healthy adults is wide, and where you fall in it is genuinely unknown without testing. Every number here inherits that uncertainty.
- Your own sleep cycles. Ninety minutes is a population average; real cycles run 70 to 120 minutes and vary night to night, which is why bedtimes are shown as windows.
- The caffeine in the cup in front of you. Brew strength and cup size move filter coffee from 70 to 140 mg. The presets are central values from a range, not measurements.
- The effect of medication or liver impairment. Some drugs change caffeine clearance far more than anything modelled here. This tool does not attempt them.
- Anything about safety. It estimates sleep impact, and nothing it says bears on driving, operating machinery, or a cardiac question.
An educational estimate, not medical advice. Talk to a clinician about sleep or cardiac concerns.
Put this on your own site
The calculator embeds as a single iframe. It carries no ads, no analytics and no cookies inside the frame — it will not add anything to your page that you have not chosen — and it works on a phone at any width.
<iframe src="https://caffeinecurfew.com/embed" width="100%" height="1650" style="border:1px solid #e1e0d9;border-radius:12px" loading="lazy" title="Caffeine cutoff calculator"></iframe>
<p><a href="https://caffeinecurfew.com/">Caffeine Curfew</a></p> Set a starting point with the same options the page uses — for example a cold brew drinker with an eleven o'clock bedtime: /embed?bed=23:00&usual=cold-brew
The frame is tall enough for the chart at the narrowest width a phone will give it, so a wide column gets some slack at the bottom. The credit line under the frame is the only thing we ask for; please keep it.
References
Written by Toni Ristola — Built the calculator and wrote the explainers. Not a clinician.
Last updated 2026-08-30