Caffeine Half-Life Calculator: How Much Is Still in You at Bedtime?

Caffeine has a half-life of roughly 5 hours in healthy adults, so half of your 15:00 coffee is still circulating at 20:00 — and a quarter of it at bedtime. Enter your dose and times below to see the milligrams still active when you try to sleep, and when your level falls low enough to stop mattering.

Reference doses: espresso ~65 mg, filter coffee ~95 mg, energy drink 80–160 mg, black tea ~45 mg, cola ~35 mg, pre-workout often 150–300 mg.

What does the evidence say about caffeine and sleep timing?

The key experiment is Drake and colleagues (2013): 400 mg of caffeine taken 0, 3 or even 6 hours before bed all produced measurable sleep disruption — the 6-hour dose cut objectively measured sleep by more than an hour, while participants underestimated the damage. That is the practical case for a hard caffeine cutoff 8–10 hours before bedtime if you take meaningful doses.

The ~5-hour half-life figure comes from classic pharmacokinetics: Statland and Demas (1980) measured a mean serum half-life of about 5.7 hours in healthy adults, and the comprehensive Fredholm review puts the typical range at roughly 3–7 hours. Caffeine blocks adenosine receptors — adenosine being the molecule that accumulates during the day and makes you sleepy — so residual caffeine at bedtime directly opposes the pressure to fall asleep.

Why does caffeine hit some people so much harder?

Clearance runs through the liver enzyme CYP1A2, and its speed varies enormously. Slow-metabolizer variants of the CYP1A2 gene are common; oral contraceptives can roughly double the half-life; pregnancy can push it far higher; smoking accelerates it; and liver disease slows it dramatically. That is why the calculator lets you pick 4, 5 or 6 hours — and why your own data beats any average. If afternoon espresso wrecks your night while your friend sleeps fine, you are probably both normal.

Caffeine also props up evening cortisol — see how that plays against your natural cortisol curve, which is supposed to be near its floor at night.

How do you find your personal caffeine cutoff?

Run it as an experiment instead of a guess: keep your total caffeine identical for two weeks, but move the last dose to before noon in week two, and compare sleep-onset latency and deep-sleep minutes from your wearable. BioTrakk structures exactly this as an n-of-1 experiment — log each coffee by chat ("espresso at 15:30"), sync your Oura or WHOOP sleep data, and get a significance-tested verdict instead of a vibe. If the cutoff helps, pairing it with glycine before bed is a sensible next test, and our supplement timing chart covers when everything else should be taken.