Avoid caffeine after 2 p.m

Cost: No cost involved. People accustomed to drinking coffee in the afternoon must summon some willpower to abstain.
In plain terms: Consuming a large cup of coffee containing 400 mg of caffeine 6 hours before bedtime reduces measured total sleep time by over 1 hour, yet personal sleep logs show no difference. To avoid any impact on sleep, a regular cup of coffee (107 mg of caffeine) must be consumed at least 8.8 hours prior to bedtime; for those going to bed at 11 p.m., 2 p.m. marks the cutoff point.
Benefit: Intake of 400 mg of caffeine 6 hours before sleep results in a measurable reduction of 1.1–1.2 hours in total sleep time compared to placebo consumption. Multiple studies combined via meta-analysis indicate that caffeine on average shortens total sleep duration by 45 minutes and lowers sleep efficiency — the proportion of time spent actually asleep while in bed — by 7%.
Evidence grade: A
Sources: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
Notes: The sole study by Drake utilized a relatively high caffeine dose of 400 mg, equivalent to roughly two or three cups of coffee, and was conducted in a single laboratory setting. Individuals with slower caffeine metabolism must adhere to an even earlier cutoff time. This recommendation complements the third item, which advises aiming for 7–8 hours of sleep nightly.