The short version
Stop drinking coffee 6 to 8 hours before your bedtime. That is the starting rule. Then adjust it for your own body using the four steps below: do the half-life math, figure out whether you clear caffeine fast or slow, set a real clock time, and test it for two weeks until you fall asleep within 20 minutes most nights.
Before you start
The honest answer to "what time should I stop drinking coffee" is not a single hour for everyone, because how long caffeine lingers depends heavily on your genetics and your bedtime. You need two numbers: your usual bedtime, and a rough sense of whether you are a fast or slow caffeine metabolizer. Caffeine works by blocking adenosine, the molecule that builds up while you are awake and creates pressure to sleep[1]. As long as caffeine occupies those receptors, your brain does not register how tired it actually is. That is the whole reason an afternoon coffee can leave you lying awake at midnight even when you feel exhausted.
Step 1 - Do the caffeine half-life math
Caffeine has an average half-life of about 5 hours in healthy adults, with a real-world range of roughly 2 to 10 hours[2].
Half-life is the time your body takes to clear half a dose. So a single 200mg coffee (about one large brewed cup) drops to 100mg after 5 hours, 50mg after 10 hours, and 25mg after 15 hours. Run the clock from when you drink it.
Drink that 200mg coffee at 2pm and you are still carrying around 50mg at midnight. A controlled trial found that 400mg of caffeine taken even 6 hours before bed cut total sleep time by more than an hour, with people often not noticing the damage themselves[3]. The residual dose does not have to feel like a jolt to fragment your sleep.
Count backward from your bedtime in 5-hour blocks. Whatever is left in your system above roughly 25mg at lights-out is the part working against you.
Step 2 - Run the fast-vs-slow metabolizer self-test
Most caffeine is broken down by a liver enzyme called CYP1A2, and a common variant in the gene that codes for it splits people into fast and slow metabolizers[4].
You do not need a genetic test to get a workable read. Pay attention to your real response over a few days:
- A 4pm coffee leaves you wired at 11pm, your heart feels fast, or you wake repeatedly: you likely lean slow.
- You can drink coffee at dinner and fall asleep at your normal time: you are probably fast.
- You feel almost nothing from a single cup and reach for a second: also a fast-metabolizer pattern.
Slow metabolizers process caffeine at roughly half the speed, so the same cup lingers far longer[5]. Older adults also tend to be more sensitive to a given dose, and that sensitivity shows up most at night[6]. If you are not sure which group you fall in, assume slow and give yourself the wider buffer. The downside of stopping coffee an hour too early is small. The downside of a wrecked night is not.
Step 3 - Apply the 6-to-8-hour rule and adjust
Start with the standard recommendation: stop caffeine 6 to 8 hours before bed[7]. For a 10pm bedtime that means a last cup between 2pm and 4pm.
Now shift it based on Step 2:
- Fast metabolizer: pull the cutoff in to 5 to 6 hours before bed (last cup around 4pm to 5pm for a 10pm bedtime).
- Average: hold at 6 to 8 hours.
- Slow metabolizer, caffeine-sensitive, or older: push the cutoff out to 8 to 10 hours (last cup around noon to 2pm).
Set the actual clock time, not a vague intention. Write it down. If your last coffee is currently a 5pm pick-me-up and you are a slow metabolizer with a 10pm bedtime, that habit alone could be the reason you stare at the ceiling.
This is also where matcha or a half-caf can bridge the gap. Matcha delivers caffeine alongside L-theanine, which blunts the jittery edge without removing the alertness[8]. If you want the swap rationale, see the matcha switch and a fuller look at why coffee may be your sleep issue.
Step 4 - Test, track, and lock your personal cutoff
Hold your chosen cutoff time fixed for two weeks. Changing it nightly tells you nothing.
Each night, note two things: how long you took to fall asleep, and how many times you woke up. If you are still taking more than 30 minutes to drop off most nights, move the cutoff 1 hour earlier and run another two weeks. Repeat until you fall asleep within about 20 minutes on most nights. That clock time is your personal cutoff.
One caution as you dial it back: pulling your caffeine earlier or cutting the total amount can trigger a withdrawal headache and a few foggy days, which usually peak within the first day or two and pass within a week[6]. Tapering by half a cup at a time is gentler than quitting cold.
A handwritten note works. So does any sleep or food-logging tool. The piece worth watching is the link between an afternoon drink and that night's sleep, which is exactly the food-to-feeling pattern that apps like Aloe AI and dedicated sleep trackers such as Whoop are built to surface. The number that matters is not how much caffeine you drank but how late, lined up against how you slept. For the manual version of that loop, see how to track food and feeling.
A worked example
Maya goes to bed at 10:30pm and feels groggy every morning despite eight hours in bed. Her last coffee is a 3:30pm latte, about 150mg.
Half-life math: 150mg at 3:30pm is roughly 75mg at 8:30pm and about 50mg at 10:30pm. Her self-test flags her as slow: a single afternoon cup leaves her heart racing into the evening. That residual 50mg at lights-out is the problem.
She moves her cutoff to 1pm (9.5 hours before bed) and holds it for two weeks. Sleep latency drops from 45 minutes to about 15. The morning grogginess fades because she is finally getting uninterrupted deep sleep instead of a caffeine-thinned version of it. Her personal cutoff is 1pm, earlier than the generic rule, because her body clears caffeine slowly.
When to see a professional
A coffee cutoff fixes caffeine-driven insomnia, not every sleep problem. Talk to a clinician if you still cannot sleep after two weeks of a caffeine-free evening, if you wake gasping or your partner reports loud snoring or pauses in breathing, or if daytime sleepiness is severe enough to affect driving or work. Persistent insomnia, restless legs, and sleep apnea need evaluation rather than another dietary tweak. Also flag it to your doctor if caffeine triggers a racing or irregular heartbeat, since slow metabolizers can be more vulnerable to caffeine's cardiovascular effects[4].
