Sleep & wake-up
Caffeine half-life calculator
Enter how much caffeine you had and when, plus your bedtime, to estimate how much is still in your system when you turn in.
Caffeine has a half-life of about 5 hours, so roughly half is cleared every 5 hours. Under 50 mg at bedtime is usually fine for most people.
How caffeine clears your system
Caffeine has a half-life of about five hours in a typical healthy adult. That means roughly half of a dose is gone after five hours, half of what remains is gone after another five, and so on. A coffee in the afternoon can still leave a meaningful amount in your bloodstream at bedtime. This tool multiplies your servings by the dose, then halves that amount for every five hours between your last drink and bed.
| Hours before bed | Share of dose remaining |
|---|---|
| 0 hours | About 100% |
| 5 hours | About 50% |
| 10 hours | About 25% |
| 15 hours | About 12% |
Reading your result
As a rough guide, under 50 mg left at bedtime is unlikely to bother most sleepers, while more than 100 mg often makes falling and staying asleep harder. Half-life varies with genetics, pregnancy, some medications and how often you consume caffeine, so treat the number as an estimate. If evenings feel wired, move your last cup earlier rather than cutting caffeine altogether.
Frequently asked questions
What counts as a serving?
Use the dose field to match your drink. A brewed coffee is often around 95 mg, espresso near 65 mg per shot, tea 30 to 50 mg and many energy drinks 80 mg or more. Adjust the per-serving value to fit what you actually drank.
Why does a five-hour half-life matter so much?
Because caffeine clears slowly, an afternoon dose carries over into the evening. A 200 mg coffee at 3 pm still leaves roughly 100 mg at 8 pm, which is enough to delay sleep for sensitive people.
Is the estimate exact for everyone?
No. Half-life ranges widely between people and can be longer during pregnancy or with certain medications, and shorter in heavy smokers. Use the figure as a guide and watch how your own sleep responds.