Caffeine calculator
Pick a drink, the time you had it and your bedtime: the calculator shows how much caffeine is still in you when you go to sleep, and whether that is likely to affect your sleep.
Try it
Had at 3 pm, about 33 mg is still in you at an 11 pm bedtime. That should not affect most people’s sleep.
Your whole day, every drink, in the free CaffeineIQ check. The iPhone app is coming soon.
How the calculator works
Caffeine does not hit you all at once and it does not vanish at a fixed time. After a drink it is absorbed over roughly the first hour, so the amount in your blood climbs to a peak. From then on your liver clears it at a steady proportional rate: for an average adult, half of whatever is left is gone about every 5 hours. That is the caffeine half-life.
The calculator runs that model for the drink you choose, minute by minute across the day, and draws it as the dot chart above. The number that matters for sleep is the one at your bedtime, and the shaded band is the night you spend asleep. Columns turn amber while you are asleep and still above the 50 mg line most people sleep fine under.
It is an estimate. Your own half-life can be anywhere from about 3 to 7 hours, and longer in pregnancy or with some medicines. The accuracy questions on the main tool adjust it for you.
One cup of coffee at different times
An 8 fl oz cup of brewed coffee has 95 mg of caffeine. Here is what is left at three common bedtimes depending on when you drink it.
| Had at | 10 pm bed | 11 pm bed | Midnight bed |
|---|---|---|---|
| 7 am | 13 mg | 11 mg | 9.6 mg |
| 9 am | 17 mg | 15 mg | 13 mg |
| 11 am | 22 mg | 19 mg | 17 mg |
| 1 pm | 29 mg | 25 mg | 22 mg |
| 3 pm | 38 mg | 33 mg | 29 mg |
| 5 pm | 51 mg | 44 mg | 38 mg |
| 7 pm | 67 mg | 58 mg | 51 mg |
The rule of thumb that falls out of it: finish your last full cup of coffee about 8 to 10 hours before bed if you want to be under 50 mg, and earlier if you are sensitive. Bigger drinks need more time; see when to stop drinking coffee.
Check your whole day
Most people have more than one drink. The free check on the CaffeineIQ home page takes every drink and the time you had it, shows the total on the same chart, and tells you the latest time for one more. It runs in your browser and keeps nothing on a server.
FAQ
How does the caffeine calculator work?
It adds up caffeine as your body absorbs it over the first hour and removes it at a steady rate, so that half is gone about every 5 hours. The result is the amount still in you at the bedtime you pick.
How much caffeine at bedtime is too much?
Most people sleep fine with less than about 50 mg in their system at bedtime. Very sensitive people may notice 25 mg; others are not bothered until about 100 mg.
Can I add more than one drink?
Yes. The free check on the CaffeineIQ home page takes your whole day, every drink and time, and shows the total at bedtime.
Look up a drink
- Starbucks Cold Brew
- Red Bull
- Coca-Cola
- Monster Energy
- Celsius
- Coffee
- Espresso
- Starbucks Pike Place Roast
- Diet Coke
- Green Tea
- All 308
Estimates, not medical advice. How it works.