Set a caffeine cutoff time based on your half-life

Caffeine has a 5–7 hour half-life — a 2 pm cup means one-quarter of it is still in your system at midnight.

Why it works

Caffeine is metabolized primarily by CYP1A2 in the liver, with a population-average half-life of about 5–7 hours (range: 2–12 hours depending on genetics, hormonal status, and medications). This means caffeine consumed at 2 pm still occupies adenosine receptors at 11 pm, delaying the adenosine-driven sleepiness signal that is needed to initiate and deepen sleep. Even if you can fall asleep, caffeine reduces slow-wave (deep) sleep, which is the most physically restorative stage.

How to do it

1. Calculate your cutoff: subtract two half-lives (~12 hours) from your target bedtime.
2. For a 10 pm bedtime and average metabolism, that is approximately 10 am–noon as the last dose.
3. Adjust based on personal experience — if you sleep poorly after a 2 pm cup, move the cutoff earlier.
4. Consider a genetic test for CYP1A2 if caffeine sensitivity feels unusually high or low.

Evidence

Walker (2017) summarizes research showing caffeine in the afternoon reduces slow-wave sleep depth even in people who report no trouble falling asleep. The half-life pharmacokinetics are well-established clinical pharmacology. (observational)

Individual caffeine metabolism varies by up to 6-fold depending on CYP1A2 genetics and other factors; a single cutoff time does not fit everyone.

Sources

• Drake et al. (2013), caffeine effects on sleep taken 0, 3, or 6 hours before bedtime, Journal of Clinical Sleep Medicine

Common mistake

Judging the cutoff by sleep-onset difficulty alone — caffeine can allow you to fall asleep while still degrading deep sleep quality, leaving you underrecovered without knowing why.