Caffeine Calculator
Add the coffee, tea, soda and energy drinks you have had today and when. See how much caffeine is in your system right now, how much will be left at bedtime, and when it drops low enough not to affect sleep.
Today’s drinks
How to track your caffeine
- Add each drink you have had today and the time you had it. The caffeine amount fills in automatically; change it if your drink is bigger or stronger.
- Set your usual bedtime, and pick a different half-life if you know caffeine stays with you longer or shorter than average.
- Read how much is in your body now and at bedtime. If too much will be left, the tool suggests the latest time for your last cup.
How long does caffeine last?
Caffeine is absorbed within about 45 minutes, peaks after roughly an hour, then leaves the body slowly. Its half-life, the time for half of it to be cleared, averages about five hours in healthy adults but ranges from under three to more than eight. So a 200 mg coffee at 3 pm still leaves around 100 mg at 8 pm and 50 mg at 1 am. That can delay falling asleep and reduce deep sleep even if you do not feel wired.
Smoking speeds up caffeine clearance; pregnancy, oral contraceptives, some antibiotics and liver conditions slow it down a lot. Genetics also matter: some people are naturally “slow metabolizers”.
How much caffeine is in common drinks?
| Drink | Typical caffeine |
|---|---|
| Brewed coffee, 8 oz | 80–100 mg |
| Espresso, 1 shot | 63 mg |
| Cold brew, 12 oz | 150–200 mg |
| Black tea, 8 oz | 40–50 mg |
| Green tea, 8 oz | 25–30 mg |
| Cola, 12 oz | 30–45 mg |
| Energy drink, 8.4 oz / 16 oz | 80 / 160 mg |
| Decaf coffee, 8 oz | 2–15 mg |
Coffee shop sizes vary widely: a large brewed coffee can contain 300–400 mg. Check the brand’s nutrition information for exact amounts.
How much is too much?
The US FDA and European Food Safety Authority consider up to 400 mg a day safe for most healthy adults, and up to 200 mg a day during pregnancy. Single doses above about 200 mg (around 3 mg per kg of body weight) are more likely to cause jitters, a racing heart or anxiety. Teens and people with heart conditions or anxiety should have less.
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Frequently asked questions
When should I stop drinking coffee to sleep well?
For most people, about 8 hours before bed. Sleep researchers have found that 400 mg even 6 hours before bedtime cut total sleep by about an hour.
Is the calculation exact?
No. It uses an average absorption rate and the half-life you choose. Your body may clear caffeine faster or slower, so use it as a guide.
Does decaf have caffeine?
A little: usually 2–15 mg per cup, enough to matter only if you drink a lot or are very sensitive.
Does the tool remember my drinks?
No, the list starts fresh each time you open the page. Nothing is saved or sent anywhere.
Is anything sent to a server?
No. Everything is calculated in your browser, and nothing you enter leaves your device.