Sleep calculator / Caffeine calculator
Caffeine Cutoff Calculator
See how much caffeine will still be in your system at bedtime, and the latest time you can have that drink.
- 100% free
- No sign-up
- No app
Typical amounts. Check the label; strength varies a lot.
Pregnancy, some medications and genetics can make caffeine last much longer.
How long does caffeine stay in your body?
Caffeine has a half-life of around 5 hours in a typical healthy adult. That means 5 hours after a 95 mg coffee, about 48 mg is still in your bloodstream; after 10 hours, about 24 mg. The real number varies a lot from person to person. Genetics, smoking, pregnancy, liver health and some medications can make it much shorter or much longer.
Why a 3 PM coffee can still hurt your sleep
Caffeine works by blocking adenosine, the chemical that builds "sleep pressure" through the day. Even if you fall asleep fine, leftover caffeine can make your sleep lighter and shorter. In one sleep-lab study, a 400 mg dose taken 6 hours before bed still cut total sleep by more than an hour, and many people didn't notice.
How the calculator works
It multiplies the caffeine in your drink by the number of servings, then halves it once per half-life until your bedtime. The latest time is when that drink would drop below about 25 mg by bedtime. That isn't an official limit, but it's a sensible cutoff: roughly the caffeine in a small cup of green tea.
How much caffeine is too much?
The FDA says up to 400 mg a day is generally not linked to negative effects for healthy adults. That's about four 8 oz cups of brewed coffee. The calculator warns you if you go over. For sleep, though, when you drink it matters as much as how much.
Easy ways to cut back
- Move your last caffeinated drink earlier by an hour a week.
- Switch the afternoon cup to half-caf, green tea or decaf.
- Check energy drinks and pre-workouts. They can carry two to three coffees' worth.
Frequently asked questions
What time should I stop drinking coffee?
For a single 8 oz coffee and a 10:30 PM bedtime, the calculator suggests a cutoff around 1 PM for an average person. A common rule of thumb is no caffeine within 8 hours of bed. Stronger drinks or higher sensitivity mean an earlier cutoff.
Does decaf have caffeine?
A little, usually a few milligrams per cup. That is well below the level that tends to affect sleep for most people.
Why can I fall asleep after coffee?
Falling asleep is not the whole story. Caffeine in your system can still reduce deep sleep and total sleep time even when you drift off easily.
Related reading
- How Much Caffeine Is in Your Drink? A Chart, Plus Your Cutoff TimeCaffeine in coffee, espresso, tea, soda and energy drinks side by side, plus the latest time to drink each one for a 10:30 PM bedtime.3 min read
- Does Green Tea Keep You Awake? Caffeine, L-Theanine and TimingOne cup of green tea has about 28 mg of caffeine, so it rarely wrecks sleep, but several cups or matcha can. Here's the latest time to drink it.3 min read
- Drank Coffee Too Late? How to Fall Asleep AnywayNothing flushes caffeine out faster, so the honest fix is to wait it out well. Here's how much is left, when it clears, and what actually helps tonight.3 min read
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These results are general estimates, not medical advice. Everyone's sleep is a little different. If you're often exhausted despite enough time in bed, snore loudly, or have been told you stop breathing in your sleep, see a doctor.