Caffeine and sleep — how late is too late?
Short answer: Caffeine's half-life is roughly 5 hours, and in a controlled study 400 mg taken six hours before bed still reduced sleep by about an hour. A practical rule is no caffeine after about 2 pm if you sleep at 10–11 pm, then adjust based on your own data.
What the research says
- In the Drake et al. (2013) study, 400 mg of caffeine (about two to three strong coffees) taken 0, 3 or 6 hours before bed all disrupted sleep. Even at 6 hours it cut total sleep by about an hour.
- A 2023 meta-analysis found caffeine reduced total sleep and deep sleep and made it take longer to fall asleep (Gardiner et al.).
A practical cutoff
| Bedtime | Last caffeine |
|---|---|
| 10:00 pm | ~2:00 pm |
| 11:00 pm | ~3:00 pm |
| Midnight | ~4:00 pm |
Sensitivity varies a lot between people, so treat this as a starting point.
Find your own cutoff
- For two weeks, tag Late caffeine whenever you have caffeine after 2 pm.
- Compare your sleep duration and next-morning recovery on tagged versus untagged days.
- Move your cutoff earlier or later based on what you see.
Pulse Coach does step 2 for you. Its impacts show “Late caffeine: −X% sleep that night” once a tag has shown up at least three times.
Questions people also ask
Does decaf affect sleep?
Decaf has a small amount of caffeine, usually a few milligrams a cup. It's rarely a problem unless you drink many cups late.
I can fall asleep after espresso. Am I immune?
Falling asleep isn't the whole story. Caffeine can reduce deep sleep and total sleep even when you drift off fine. Check your sleep stages and next-day HRV.
Sources
Not medical advice. This article is general information about wellness metrics. It is not a diagnosis or a substitute for professional care. If a reading worries you, or you feel unwell, talk to a doctor.