Caffeine half-life calculator

The short answer: caffeine has a half-life of about 5 hours in most adults - so half of your 2 pm coffee is still working on you at 7 pm, and a quarter at midnight. Dial in your day below to see your bedtime number.

WHAT DID YOU DRINK?
HOW MANY?
LAST ONE AT
YOUR METABOLISM
BEDTIME
IN YOUR BLOOD AT 11 PM
55
mg caffeine
Roughly a full espresso (0.9×) still circulating. Most people’s sleep is measurably lighter at this level.
2 pm
3 pm
4 pm
5 pm
6 pm
7 pm
8 pm
9 pm
10 pm
11 pm
12 am
1 am
caffeine remaining through the evening · sage bar = your bedtime

How long does caffeine stay in your system?

Caffeine's half-life in healthy adults ranges from 3 to 7 hours, averaging about 5. Every half-life, the amount in your blood halves - it doesn't just "wear off" when the buzz fades. A 95 mg cup at 2 pm leaves ~48 mg at 7 pm, ~24 mg at midnight, and ~12 mg at 5 am. Full clearance of a morning coffee takes roughly a day.

Time after your cup
Caffeine left
Of a 95 mg coffee
Right away
100%
95 mg
5 hours
50%
48 mg
10 hours
25%
24 mg
15 hours
12.5%
12 mg
20 hours
6%
6 mg

Your personal half-life is largely genetic (the CYP1A2 enzyme), and it stretches with pregnancy, some medications, and liver load - and shrinks for smokers. That's why the same latte wrecks one person's sleep and doesn't touch another's.

What's a good caffeine cutoff time for sleep?

Research on 100 mg+ doses shows measurable sleep disruption when caffeine is taken up to 6 hours before bed - for an 11 pm bedtime, that's a 5 pm hard stop, and 2 pm is the safer line for average metabolizers. But that's a population average, not your number. Slow metabolizers may need a noon cutoff; fast ones can genuinely handle an after-dinner espresso.

This calculator shows the average. You aren't average.

The honest way to find your cutoff: log your caffeine timing and sleep for two weeks, then compare the numbers. Claritips does exactly that - one 60-second check-in a day, and a verdict like "sleep during the experiment: 4.1★ vs 2.9★ before." No AI, just your own arithmetic.

Run the 14-night caffeine test →

Common questions

Does this apply to tea and energy drinks too?
Yes - caffeine is caffeine. Only the starting dose differs: black tea ~47 mg, green tea ~28 mg, a typical energy drink 160 mg, cold brew often 200 mg+. Pick the closest drink above and the math is identical.
Why do I sleep fine after an evening espresso?
You may be a genetically fast metabolizer (CYP1A2), or caffeine may be masking sleep pressure without blocking sleep itself. Note that studies still show reduced deep sleep even when people fall asleep fine - you can feel unaffected and still wake less rested.
Is 400 mg a day really the safe limit?
That’s the FDA’s general guidance for healthy adults (about 4 cups of coffee). It’s a daily-intake guideline, not a sleep guideline - timing matters more than total for how you sleep.
How accurate is this calculator?
It’s honest population math: exponential decay with the half-life you choose. What it can’t know is your personal half-life or sensitivity - the two-week self-test is how you find those.
METHOD How this is calculated - the formula, the constants and the limits →
RELATED GUIDES
CAFFEINECaffeine after 2 pm: what your own numbers will showSLEEPHow to fall asleep faster: nine methods that actually have evidenceENERGYWhy is my energy so low? Nine honest causes - and how to find yours
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