How Many Hours Before Bed Should You Stop Drinking Coffee? Work Back From Your Bedtime

How caffeine gets in the way of sleep

While you're awake, a substance called adenosine builds up in your brain and creates sleep pressure. Caffeine works by blocking the receptors that adenosine binds to, so you feel less sleepy. That's handy for fighting daytime drowsiness, but if caffeine is still in your body at bedtime, the same mechanism interferes with sleep.

• It takes longer to fall asleep
• Deep sleep (the deep stages of non-REM sleep) decreases and sleep becomes lighter
• You're more likely to wake up during the night
• Even if you feel you slept fine, measurements show your total sleep time is shorter

In a study that compared 400 mg of caffeine taken 0, 3 and 6 hours before bed, total sleep was about an hour shorter even when it was taken 6 hours before. The larger the dose, the earlier you need to stop. Conversely, a small amount may have little effect even a few hours before bed. Rather than setting a fixed “N hours before bed,” it is more realistic to think in terms of how many mg are still in your body when you go to sleep.

If you drink at this time, how many mg are left at bedtime?

This is how much caffeine remains in your body at bedtime if you drink only one cup of drip coffee (about 90 mg in 150 ml) and go to bed at 11 p.m. The calculation includes the time it takes to be absorbed.

For someone with a typical 5-hour half-life, a cup 6 hours before bed has dropped to about 41 mg, so the “6 hours before bed” rule roughly holds. But for slow metabolizers (a half-life of 8–10 hours), close to 40–50 mg remains even when they drink 9 hours before bed. If you feel that “coffee in the late afternoon keeps me up,” you may be this type.

Chart: the latest time for your last cup, worked back from bedtime

These are the latest times you can drink one cup of drip coffee (about 90 mg) and still be at 50 mg or less at bedtime, assuming no other caffeine that day.

For a typical person, the last cup should be about 4.5 hours before bed. If you set the target at 25 mg or less (for light sleepers), the last cup for an 11 p.m. bedtime moves earlier to 5:12 p.m. with a 3-hour half-life, 1:30 p.m. with 5 hours and 7:58 a.m. with 8 hours. If you metabolize caffeine slowly and also sleep lightly, “coffee in the morning only” is the realistic choice.

Green tea, black tea, energy drinks: what's the cutoff?

Using the same approach, these are the latest times a typical person (5-hour half-life) going to bed at 11 p.m. can have one serving and stay at 50 mg or less at bedtime.

Black tea and sencha come in small servings, so one cup alone stays under the guideline even in the evening. Of course, if you keep refilling from the teapot it adds up: one cup of sencha each at 2, 4 and 6 p.m. leaves about 29 mg at 11 p.m. Gyokuro has about 2.7 times as much caffeine per 100 ml as coffee, so even a small cup can equal a cup of coffee.

For a second or third cup, assume the earlier ones are still there

The chart assumes only one cup that day. If you've already had coffee in the morning, what's left of it moves your cutoff earlier. Here is a comparison for a typical person going to bed at 11 p.m. (5-hour half-life, 50 mg target).

Just one cup in the morning moves your second-cup cutoff about 2 hours earlier. On a day with coffee in the morning and at lunch, even a third cup at 12:30 p.m. puts you over 50 mg at 11 p.m., so it's safer to switch to decaf or barley tea in the afternoon. For more on how caffeine accumulates, see how long caffeine stays in your system.

Using caffeine for night shifts or late-night studying

On a night shift or when cramming before an exam, you need to think about both the hours when you want caffeine to keep you awake and the hours afterward when you want to sleep. For example, if a typical person drinks a 355 ml energy drink (about 142 mg) at 9 p.m., it decreases like this.

• If you sleep from 9 a.m. after a night shift, one can at 9 p.m. works out to about 28 mg when you go to bed. Adding more after 2 a.m. leaves a lot in your body when you want to sleep.
• To fight sleepiness, drink it 30 minutes to an hour before you need it to work. It takes about an hour to peak.
• Don't drink several cans at once; keep a single dose under 200 mg. Two 355 ml energy drinks in a row add up to about 284 mg.
• Even when cramming, cutting sleep impairs memory consolidation. Caffeine can only cover sleepiness; it is not a substitute for sleep.

Work out “how late can I have one more cup?” with the tool

1. 1

   Enter what you've drunk today

   Enter every drink and time since the morning. For cans and bottles, use “Other” and match the mg on the label for accuracy.

2. 2

   Enter when you woke up and when you'll go to bed

   If you go to bed after midnight, just enter it as is, such as “0:30,” and it is calculated as the next day.

3. 3

   Choose your metabolism (half-life) and target amount

   If you know late-afternoon coffee keeps you awake, try a half-life of 8 hours and a target of 25 mg.

4. 4

   Check “If I have one more cup, by what time?”

   Choose the drink you want next, and it shows the latest time that keeps the amount at bedtime under your target. If that's no longer possible, it shows “Skip it for today.”

The total for the day is shown at the same time, so check the amount itself too. How many mg a day is OK is explained in the daily caffeine limit.

FAQ

How many hours before bed should I stop drinking coffee?

For one cup of drip coffee (about 90 mg), a typical person (5-hour half-life) will be at 50 mg or less at bedtime if they drink it about 4.5 hours before bed. For an 11 p.m. bedtime, that's around 6:30 p.m. Slow metabolizers need about 7 hours, and on days you've already had coffee in the morning or at lunch, the cutoff moves even earlier. Think of the common “6 hours before bed” rule as a guideline with a little margin.

Why can't I sleep after drinking coffee in the late afternoon?

You may have a long caffeine half-life. If someone with an 8-hour half-life drinks one cup of drip coffee at 4 p.m., about 50 mg is still there at 11 p.m. What you drank in the morning also remains, so a late-afternoon cup pushes the amount at bedtime higher. Switching to decaf or barley tea in the afternoon can help.

Is it OK to drink green tea or black tea before bed?

One cup of sencha (about 24 mg in 120 ml) or black tea (about 45 mg in 150 ml) won't exceed the 50 mg bedtime guideline on its own. Gyokuro, however, has about 96 mg in 60 ml, about the same as coffee, so avoid it at night. If you sleep lightly or drink several cups, caffeine-free drinks such as barley tea or rooibos are a safer choice than hojicha.

How late can I drink an energy drink and still sleep?

For a typical person going to bed at 11 p.m., a 250 ml product (about 80 mg) should be finished by around 7:20 p.m., and a 355 ml product (about 142 mg) by around 3 p.m., to stay at 50 mg or less at bedtime. The amount varies by product, so calculate using the mg of caffeine printed on the can.

If I can still fall asleep after caffeine, does that mean it has no effect?

Even if you fall asleep, your sleep may be lighter or shorter. One study found that 400 mg taken 6 hours before bed cut sleep by about an hour without the participants noticing. If daytime sleepiness won't go away, try reducing how much is left in your body at night.