Avoid caffeine after about 2 p.m. if you go to bed at 11 p.m.
Taking 400 mg of caffeine six hours before bed shortened objectively measured sleep by over an hour, although sleep diaries did not detect the difference. The pooled estimate suggests finishing an ordinary 107 mg coffee at least 8.8 hours before bedtime; for an 11 p.m. bedtime, that is about 2 p.m.
What it takes
Free. Afternoon coffee drinkers need to change a habit.
What you may gain
Caffeine at 400 mg six hours before bed reduced instrument-measured total sleep by 1.1–1.2 hours versus a caffeine-free placebo drink, without a corresponding diary-reported difference. A meta-analysis found an average 45-minute reduction in total sleep and a 7% reduction in sleep efficiency, the proportion of time in bed spent asleep. Its estimate for avoiding sleep disruption from a 107 mg coffee was a cutoff at least 8.8 hours before bed.
Context & considerations
Drake's study was from one laboratory and used a relatively high dose, roughly two or three coffees. Slow metabolizers may need an earlier cutoff. The benefit is recovered sleep time and overlaps with getting enough sleep.
Research & references
Drake, Roehrs, Shambroom & Roth (2013). Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed. Journal of Clinical Sleep Medicine. https://doi.org/10.5664/jcsm.3170 ; Gardiner et al. (2023). The effect of caffeine on subsequent sleep: A systematic review and meta-analysis. Sleep Medicine Reviews. https://doi.org/10.1016/j.smrv.2023.101764