Time caffeine to protect the second half of your day

Stop caffeine 8–10 hours before bed so it has cleared before sleep.

Why it works

Caffeine blocks adenosine, the molecule that builds "sleep pressure" across the day, so it masks tiredness rather than removing it. Its half-life is several hours, meaning a late afternoon coffee can leave a meaningful dose in your system at bedtime — fragmenting sleep and cutting deep sleep even when you do fall asleep.

How to do it

1. Set a daily caffeine cutoff roughly 8–10 hours before your target bedtime.
2. Account for hidden sources — tea, chocolate, pre-workout, some sodas and medications.
3. If you are sensitive, shift the cutoff earlier; sensitivity to caffeine varies widely between people.

Evidence

A controlled study found caffeine taken even 6 hours before bed significantly reduced total sleep time, and caffeine pharmacology (adenosine antagonism, multi-hour half-life) is well characterized. (rct)

Metabolism varies genetically, so the right cutoff is individual; the direction (earlier is safer) is robust.

Sources

• Drake et al. (2013), "Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed", J. Clinical Sleep Medicine

Common mistake

Judging caffeine by whether you can still fall asleep. You can fall asleep and still lose deep sleep — felt sleepiness is not the metric.