Caffeine Cutoff Calculator
The 2 pm coffee is not gone by bedtime. This works out roughly how much of it is still circulating, and shows the range rather than pretending to one number.
Caffeine cutoff calculator
How much caffeine is still circulating at bedtime, and the latest you could have had it.
8.0 hours between the drink and bed
About 63 mg still circulating at bedtime
Roughly 48 mg if you clear caffeine quickly, and 75 mg if you clear it slowly. The spread between people is larger than most calculators admit.
Over your 50 mg target
To be under 50 mg by 23:00, the latest you could have had this much is 13:22.
This models how much caffeine is left, not how it will affect you. There is no established milligram figure at which sleep is unaffected — the bedtime target is your preference, not a clinical limit.
How caffeine actually leaves your body
Caffeine follows first-order elimination, which means a fixed proportion clears per unit of time rather than a fixed amount. That gives the familiar half-life curve:
remaining = dose × 2(−hours ÷ half-life)
At a five-hour half-life, a 190 mg coffee at 3 pm leaves about 63 mg at 11 pm — not far off a shot of espresso, still going, as you get into bed.
Why we show a range instead of a number
Five hours is the textbook half-life for a healthy adult, and it is also an average hiding an enormous spread. Genotype at CYP1A2, the liver enzyme that does most of the work, varies widely between people. Smoking speeds clearance up substantially. Oral contraceptives, pregnancy and some liver conditions slow it down, in the last case dramatically.
Any calculator that returns one confident figure is hiding that variation. This one shows what a faster and a slower clearance would mean for the same drink, because for most people the honest answer is a band.
The bedtime target is your preference, not a limit
There is no established milligram figure below which caffeine reliably stops affecting sleep. The target field defaults to 50 mg because it is a round number roughly half a cup of coffee, not because a study identified it as safe. Treat it as a dial for your own experimenting.
What the research does support is that caffeine close to bedtime measurably disrupts sleep even when people do not notice it subjectively — which is exactly why an arithmetic estimate is more useful than how awake you feel. Our guide to sleep architecture covers what that disruption looks like.
What this does not model
- Absorption. It assumes the full dose is in you at the moment you drink it. In reality caffeine peaks roughly 30 to 60 minutes in, so the first hour is an approximation.
- Repeat doses. One drink at a time. Three coffees across a day stack on top of each other and clear from a higher starting point.
- Sensitivity. Two people with the same residual can sleep completely differently. This estimates what is present, not what it does to you.
If the number surprises you
The usual fix is moving the last dose earlier rather than cutting the total. If you are looking at what else moves sleep, we cover sleep supplements and the evidence behind them and the more specific case of L-theanine, which is often paired with caffeine precisely because of this problem.