Caffeine clears exponentially, and its half-life in the average person is about 5–6 hours. Let us put real numbers on it.
How much is left at midnight
Take 200 mg (a large coffee) at 3pm and a 5.5-hour half-life. By 8:30pm about 100 mg remains, and around midnight still ~50 mg — the equivalent of half an espresso sipped right before bed. You will find the decay curve and the full explanation in Caffeine and sleep.
Why “the afternoon” is the wrong cutoff
The threshold is not the time of day but the distance to sleep: 8–10 hours. Someone in bed at 10pm has a different deadline than someone who sleeps at 1am. So instead of a fixed hour, count back from your wake time — the sleep tools help with that.
The cheapest lever
Moving your last coffee two or three hours earlier costs nothing and often does more for sleep than any supplement. It is the first step before you tinker with anything else — the rest is collected in sleep hygiene.
Frequently asked questions
What time should I stop drinking coffee?
A practical rule is 8–10 hours before bed. For an 11pm bedtime that means a last coffee around 1–3pm. Slow caffeine metabolizers should move that cutoff even earlier.
Does afternoon caffeine really hurt sleep if I fall asleep fine?
Yes. In an RCT, 400 mg taken 6 hours before bed cut total sleep time even when subjects reported no trouble falling asleep. Falling asleep is not the same as sleep quality and duration.
Sources
- Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed (2013) · RCT · PMID 24235903