Caffeine calculator
Add what you drank today and when. See how much caffeine is still in your body at bedtime, and when your last cup should be.
- Today in all
- 255 mg
- Peak
- 172 mg
- Last caffeine, for a good night
- By 3:00 PM: eight hours before bed
Averages from the FDA and USDA; brews vary a lot. Caffeine takes 30 to 60 minutes to peak, which this leaves out. Not medical advice.
One coffee, and what's left at 11 PM
A 95 mg cup of brewed coffee, with a five-hour half-life:
| Drunk at | Left at 11 PM | Share of the cup |
|---|---|---|
| 8 AM | 12 mg | 13% |
| 10 AM | 16 mg | 16% |
| 12 PM | 21 mg | 22% |
| 2 PM | 27 mg | 29% |
| 4 PM | 36 mg | 38% |
| 6 PM | 48 mg | 50% |
| 8 PM | 63 mg | 66% |
A 4 PM coffee still has more than a third of its caffeine in you at 11, more than a cup of green tea.
Caffeine in common drinks
| Drink | Serving | Caffeine |
|---|---|---|
| Brewed coffee | 8 oz / 240 ml | ~95 mg |
| Espresso | 1 shot | ~63 mg |
| Latte or cappuccino | 2 shots | ~126 mg |
| Instant coffee | 1 cup | ~60 mg |
| Black tea | 8 oz / 240 ml | ~47 mg |
| Green tea | 8 oz / 240 ml | ~28 mg |
| Cola | 12 oz / 355 ml can | ~34 mg |
| Energy drink | 8.4 oz / 250 ml can | ~80 mg |
| Pre-workout or caffeine pill | 1 dose | ~200 mg |
Typical values; coffee-shop cups are often larger and stronger.
Using caffeine for focus
Caffeine works by blocking adenosine, the chemical that builds up while you're awake and makes you feel sleepy. A moderate dose before a hard task helps; a big one late in the day borrows alertness from tonight. Time your coffee for your focus block, and stop early enough that it's mostly gone by bed. Our post on caffeine and sleep goes deeper, and the sleep calculator helps with the bedtime itself.
Not medical advice. If you're pregnant or take medication, ask your doctor about caffeine.
Questions
What is caffeine's half-life?
About five hours in a typical healthy adult, which means half of a dose is still in your body five hours after you drink it, and a quarter after ten. It varies widely, from around two hours to more than eight: smoking speeds it up, while pregnancy, oral contraceptives and some medications slow it down.
When should I stop drinking coffee?
Many sleep researchers suggest stopping at least six to eight hours before bed. In a 2013 study, 400 mg of caffeine taken six hours before bedtime still cut total sleep by more than an hour, even though people didn't notice the difference.
How much caffeine is too much?
The US Food and Drug Administration says 400 mg a day, roughly four cups of brewed coffee, is an amount not generally linked to negative effects in healthy adults. Pregnant people are usually advised to stay under 200 mg. Sensitivity varies a lot from person to person.
How accurate is this?
It's an estimate. Caffeine content varies with the bean, the brew and the cup size, and absorption takes 30 to 60 minutes, which the calculator skips over. Use it to see the shape of your day, not as a precise measurement.
Further reading
- Caffeine half-life: when to have your last coffeeCaffeine's half-life is about five hours, so afternoon coffee is still working at bedtime. What's left of a cup over time, what changes it, and when to stop.
- How long should a power nap be?The best power nap is 10 to 20 minutes, or a full 90. What the research found, when to nap, how the coffee nap works, and how to nap well.
- How to study for long hours without burning outHow to study all day and still learn: work in blocks with real breaks, do the hard subject first, nap and use caffeine wisely, and protect your sleep.
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