Is caffeine 6 hours before bed bad?
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For a big dose, yes. In a 2013 study, 400 mg of caffeine taken 6 hours before bed cut more than an hour of measured sleep. For a small dose, 6 hours is more than you need. In a 2025 trial, 100 mg taken 4 hours before bed did nothing measurable.
Six hours is the number most sleep advice gives, and it comes from that 2013 study. The study tested one dose, 400 mg, which is about four 8 oz coffees taken at once. The researchers didn’t test a single cup.
We’d use 6 hours as a rule for big drinks only. For a single espresso or a tea, 4 hours is enough. For a 16 oz coffee, a CELSIUS or a pre-workout scoop, 6 hours isn’t enough, and they belong before lunch.
The study behind the 6 hours
The researchers gave 12 healthy sleepers (6 women and 6 men, aged 19 to 48) 400 mg of caffeine at bedtime, 3 hours before or 6 hours before, and a placebo on other nights. A sleep monitor at home measured 1.1 to 1.2 hours less sleep at all three times, even at 6 hours.
Their own sleep diaries at 6 hours showed a loss of 41 minutes, a gap that fell just short of statistical significance. The people lost more sleep than they noticed. The study was small, it was funded by a grant from the company that made the monitor, and the authors noted the device may undercount time awake.
What 6 hours leaves, by drink
| Drink 6 hours before bed | Caffeine | Left at bedtime |
|---|---|---|
| Black tea, 8 oz | 47 mg | about 23 mg |
| Single espresso | 63 mg | about 30 mg |
| Coffee, 8 oz | 95 mg | about 46 mg |
| Coffee, 16 oz | 190 mg | about 92 mg |
| CELSIUS, 12 oz | 200 mg | about 97 mg |
| Pre-workout scoop, average | 254 mg | about 123 mg |
| The study’s dose | 400 mg | about 193 mg |
These use the average half-life of 5 hours. An 8 oz coffee 6 hours out leaves a little over our lower bedtime line (40 mg). A 16 oz coffee leaves more than our upper line (80 mg).
What the 2025 trial added
A 2025 trial tested more than one dose. 23 healthy young men had 100 mg or 400 mg at 12, 8 or 4 hours before bed, or a placebo, on separate nights, and wore a sleep monitor at home. The 100 mg dose did nothing measurable at any of the three times. The 400 mg dose cut about 51 minutes of sleep at 4 hours, and it still cut about 21 minutes of deep sleep at 12 hours. The figure below lays out all six.
Find your time
The cutoff clock works out the latest time for your own drink and bedtime, and when should I stop drinking coffee before bed? has the table for every drink.
The cup beats the clock
6 sources
- Drake C, Roehrs T, Shambroom J, Roth T, Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed, Journal of Clinical Sleep Medicine, 2013pmc.ncbi.nlm.nih.gov
- Gardiner C and others, Dose and timing effects of caffeine on subsequent sleep: a randomized clinical crossover trial, Sleep, 2025doi.org
- Antonio J and others, Common questions and misconceptions about caffeine supplementation: what does the scientific evidence really show? Journal of the International Society of Sports Nutrition, 2024doi.org
- USDA FoodData Central, SR Legacy: brewed coffee (171890), espresso (171891), brewed black tea (173227) and brewed green tea (171917)fdc.nal.usda.gov
- CELSIUS Sparkling Fantasy Vibe, 12 fl oz can, label photographed November 2025 (caffeine content 200 mg), Open Food Facts 0889392000597, checked 2026-11-14world.openfoodfacts.org
- Jagim AR, Harty PS, Camic CL, Common Ingredient Profiles of Multi-Ingredient Pre-Workout Supplements, Nutrients, 2019doi.org
