Coffee needs a cutoff that accounts for dose

Finish ordinary coffee about eight to nine hours before bed as a starting experiment, then adjust for the amount and your sleep. A large single dose can disturb sleep even 12 hours later, so one universal cutoff cannot fit every drink or person.

The familiar nine-hour estimate comes from Carissa Gardiner and colleagues' 2023 review of 24 studies, which modelled a 250 mL coffee containing 107 mg of caffeine. Their estimated cutoff was 8.8 hours before bed; across the different doses and schedules studied, caffeine reduced sleep by about 45 minutes on average. That pooled loss does not mean every afternoon coffee removes 45 minutes, and the estimated cutoff describes an average relationship rather than a personal deadline.

Dose changes the picture: in a blinded crossover trial of 23 healthy men, 400 mg affected aspects of sleep when consumed up to 12 hours before bed. Researchers detected no significant sleep changes after 100 mg at the tested times, including four hours before bed, but that small male-only sample cannot establish a safe four-hour rule for everyone. Participants also took their usual morning caffeine, so the study tested an additional single dose.

Counting cups can conceal a large difference: the FDA lists 113–247 mg for a 12-ounce brewed coffee, more than a twofold range. Its commonly cited 400 mg daily amount concerns general safety for most adults and does not promise undisturbed sleep. Earlier drinks also contribute to the caffeine remaining at bedtime, so the final cup's timing tells only part of the story.

People clear caffeine at different speeds: EFSA gives a typical adult half-life of four hours, ranging from two to eight, with medication, pregnancy, and liver health among the influences. In a simplified calculation, 100 mg leaves 25 mg after eight hours with a four-hour half-life, but 50 mg with an eight-hour half-life. Those figures illustrate exposure rather than predict sleep quality; changed circumstances can make a previously comfortable routine stop working.

For an 11 p.m. bedtime, try finishing around 2–3 p.m. and compare several ordinary nights before changing the dose or moving earlier.