Caffeine has an average half-life of about 5 hours, so half of it is still in your body 5 hours after you drink it, and about a quarter after 10 hours. For a typical 95 mg cup of coffee, that means it takes roughly 9 and a half hours to drop below 25 mg. The buzz fades sooner, but the caffeine doesn't.
Free toolCaffeine Cutoff CalculatorHow much caffeine is still in you at bedtime, and your latest cup.What "half-life" means
Half-life is the time it takes your body to clear half of a substance. It doesn't mean caffeine is gone after two half-lives. Each 5 hours, whatever is left gets cut in half again: 95 mg becomes about 48, then 24, then 12.
That's why a morning coffee rarely affects sleep, but a mid-afternoon one can. Your liver does almost all the work, and it works at its own pace.
Timeline for one 95 mg coffee
This table shows how much caffeine is left after one 8 oz cup of brewed coffee (about 95 mg), using the average 5-hour half-life.
| Time after drinking | Caffeine left | If you drank it at 8 AM |
|---|---|---|
| 0 hours | 95 mg | 8 AM |
| 1 hour | 83 mg | 9 AM |
| 2 hours | 72 mg | 10 AM |
| 3 hours | 63 mg | 11 AM |
| 4 hours | 55 mg | 12 PM |
| 5 hours | 48 mg | 1 PM |
| 6 hours | 41 mg | 2 PM |
| 7 hours | 36 mg | 3 PM |
| 8 hours | 31 mg | 4 PM |
| 9 hours | 27 mg | 5 PM |
| 10 hours | 24 mg | 6 PM |
| 12 hours | 18 mg | 8 PM |
| 14 hours | 14 mg | 10 PM |
| 16 hours | 10 mg | 12 AM |
| 20 hours | 6 mg | 4 AM |
| 24 hours | 3 mg | 8 AM next day |
So an 8 AM coffee is down to about 14 mg by a 10 PM bedtime. The same cup at 4 PM would leave about 44 mg at 10:30 PM, nearly half a cup's worth. If you're already in that spot tonight, here's what to do when you drank coffee too late.
When do you feel it, and when does it wear off?
You usually start to feel caffeine within about half an hour to an hour, as it's absorbed. The noticeable lift tends to fade over the next few hours, well before the caffeine itself is gone.
That mismatch is the trap. You stop feeling it, assume it's worn off, and have another. But the leftover amount can still make your sleep lighter and shorter. In one sleep-lab study, a 400 mg dose taken 6 hours before bed cut total sleep by more than an hour, even though people didn't clearly notice it.
What changes how long caffeine lasts
Five hours is an average. The real number varies a lot from person to person. A major review of caffeine metabolism lists these factors:
- Genetics. Most caffeine is broken down by one liver enzyme, CYP1A2, and common gene variants make it work faster or slower.
- Smoking. Smokers tend to clear caffeine faster.
- Pregnancy and hormones. Pregnancy and some hormonal contraceptives can slow clearance.
- Liver health. Liver disease can slow it considerably.
- Medications. Several drugs interact with caffeine and can make it linger.
- Age, body weight and diet also play a part.
Here's how much the half-life matters for that same 95 mg coffee:
| If your half-life were | Time to drop below 25 mg | Left after 10 hours |
|---|---|---|
| 3 hours | 5 h 47 min | 9 mg |
| 4 hours | 7 h 42 min | 17 mg |
| 5 hours (average) | 9 h 38 min | 24 mg |
| 6 hours | 11 h 33 min | 30 mg |
| 8 hours | 15 h 24 min | 40 mg |
If coffee after lunch reliably keeps you up, you're probably at the slow end. The caffeine calculator lets you adjust for your own sensitivity.
How much is too much in a day?
The FDA says up to 400 mg a day is generally not associated with negative effects in healthy adults, roughly four 8 oz cups of brewed coffee. For sleep, though, timing matters as much as the total. Two cups at 7 and 9 AM are very different from two cups at 1 and 4 PM.
To compare coffee with tea, soda and energy drinks, see the caffeine in drinks chart.
A simple rule of thumb
- Regular 8 oz coffee: stop about 9 and a half to 10 hours before bed.
- Single espresso shot: about 7 hours.
- Black tea: about 4 and a half hours.
- Big coffee-shop sizes, energy drinks, pre-workout: make them morning-only.
- Sensitive to caffeine: add a few hours to all of the above.
The sleep calculator can help you set the bedtime to count back from.