What time should you stop drinking coffee?

Stop caffeine at least nine hours before bed for a small coffee, and longer for a big one. For an 11pm bedtime, that's a cutoff of 2pm at the latest, which is where Goodmorrow's cutoff comes from. If you go to bed before 11, drink big coffees, or caffeine hits you hard, make it earlier.

The caffeine cutoff calculator works out the time for your own bedtime and drink.

A 2023 review of 24 studies worked out that a small cup of coffee, about 100 mg of caffeine, cut total sleep if it was drunk within 8.8 hours of bed. A typical pre-workout drink, with about twice the caffeine, did the same within 13.2 hours, and a big coffee-shop coffee can hold that much caffeine too. So a large coffee is best before about 10am if you're in bed by 11.

How long does caffeine stay in your system?

Caffeine's half-life in adults is three to seven hours. That's how long your body takes to clear half of it, so at five hours, about a third of a 2pm coffee is still in you at 10pm.

How fast you clear it varies a lot. Much of the difference is genes. Smoking speeds it up, and the pill, pregnancy, some medicines and liver problems slow it down. The pill can roughly double the half-life. Some people seem fine with an espresso after dinner, partly because they clear it faster and partly because they're less sensitive to it.

How does caffeine affect sleep?

Caffeine blocks the brain's receptors for adenosine, one of the signals that builds up while you're awake and helps make you sleepy. While caffeine is still around, it dulls the sleepiness you've built up all day.

You can fall asleep fine and still sleep worse for it. In the 2023 review, where caffeine was mostly taken within a few hours of bed, it cut total sleep by 45 minutes on average, with 12 more minutes awake in the night and less deep sleep.

People often feel less of it than there is. In one small study of good sleepers, people took 400 mg of caffeine six hours before bed, about what's in two or three 12-ounce coffees, and the FDA's figure for a whole day for most healthy adults. A sleep monitor showed more than an hour less sleep. Their own sleep diaries showed a smaller loss, too small for the study to be sure of.

How much is in a drink

The FDA's typical amounts for a 12-ounce drink:

Coffee-shop sizes can hold a lot more. Decaf isn't zero either: an 8-ounce cup of decaf coffee usually has 2 to 15 mg. Caffeine also turns up in pre-workout powders, some headache pills and dark chocolate, so check the label on anything you have in the afternoon.

Do you need to give it up?

Usually not. Move it earlier. A modest morning coffee has mostly worn off by bedtime, and an afternoon one is still working.

Cutting back suddenly can give you a headache and make you tired, even if you only have a cup or two a day. It usually starts within a day and lasts two to nine days. It's easier to step down, with half-caf in the afternoon for a week, then decaf.

If you're pregnant, trying to be, or breastfeeding, or you have a health condition or take medicines, ask your doctor, midwife or pharmacist how much caffeine is right for you.

How Goodmorrow coaches it

"No caffeine after 2pm" is one of the easier habits in Goodmorrow. At 1:30 you get a nudge, something like "Coffee cutoff in half an hour." Each day you mark it done. At two weeks we look at how your nights went and, with a ring, roughly how quickly you fell asleep. A small change can be hard to see that soon, so a flat result doesn't mean caffeine leaves you alone.

If your morning notes keep mentioning a late coffee, we'll probably pick the cutoff next.