Caffeine does not leave your system all at once. Understanding how the body processes it explains why an afternoon coffee can still affect your sleep.
| Factor | Detail |
|---|---|
| Peak effect | 30 to 60 minutes after drinking |
| Half-life | About 5 to 6 hours |
| Daily limit (adults) | Up to about 400 mg |
| Pregnancy | Generally under 200 mg |
| Sensitivity | Varies with genetics, age, and tolerance |
How the half-life works
A 5 to 6 hour half-life means that about half the caffeine from a cup is still in your body five to six hours later. A coffee at 4 pm can leave a meaningful dose circulating at bedtime, which is why caffeine close to evening disrupts sleep for many people.
Cut off caffeine early. To protect sleep, stop caffeine at least 6 hours before bed. People who are sensitive may need an even earlier cutoff.
See the Caffeine Calculator and the Caffeine Content Chart.