The guide

How long caffeine lasts

By GyroscopeUpdated November 14, 20269 sources

About half of a cup’s caffeine is still in you 5 hours after you drink it, and a quarter after 10. That’s the average. In healthy adults, the time for half to go runs from 1.5 to 9.5 hours. An 8 oz coffee at 3pm still leaves about 35 mg in you at 11pm, as much as a can of Coke.

Why does caffeine feel gone when it isn’t?

The buzz comes and goes faster than the caffeine does. Almost all of a cup is absorbed within 45 minutes, and the level in your blood peaks somewhere between 15 minutes and 2 hours after you drink it. That rise is the part you notice. By evening the morning coffee feels long gone, and it’s easy to assume your body has finished with it.

People are bad at telling. In a 2025 trial in Brisbane, 23 young men took capsules of caffeine or a dummy at different times before bed on seven different nights. Asked the next morning what they’d had and when, only 22% got both right.

The whole thing in one picture

Drop a ball and each bounce comes back up a set share of the last one. Drop it from your chest and it’s soon bouncing below your ankle. Drop it from a second floor window and it keeps bouncing above your knee for a long time, even though it loses height at exactly the same rate.

Caffeine falls the same way. Every 5 hours or so, half of whatever is in you is gone, whether that’s 400 mg or 40. A bigger cup doesn’t clear faster to make up for it, so it stays above any line you draw for longer.

The math for your own day

1. The cup goes in over about 45 minutes. That’s how long it takes to absorb almost all of it.
2. Then it halves every half-life. On the average of 5 hours, that’s half by about 5¾ hours after the cup and a quarter by about 10¾.
3. Every drink counts on its own clock. Work out what each one leaves at your bedtime and add them up.

Here’s one 8 oz brewed coffee (95 mg, USDA) on a 5 hour half-life.

A 3pm cup leaves about 35 mg at 11pm, 30 mg at midnight and 20 mg at 3am. A 16 oz cup leaves twice each of those.

What each drink at 3pm leaves at 11pm

The milligrams come from USDA FoodData Central, Coca-Cola, Red Bull, and a 2019 count of the top 100 pre-workouts. The cup sets the dose has every drink and its source.

Two cutoffs, one answer

In 2023 a group of Australian sleep researchers pooled 24 studies and worked out how long before bed you’d have to stop to keep caffeine from cutting your total sleep. For a 107 mg coffee they got 8.8 hours. For a 217.5 mg pre-workout scoop they got 13.2 hours.

Those look like two different rules. Run them through the halving math and they come out the same. The coffee at 8.8 hours leaves about 35 mg at bedtime, and the scoop at 13.2 hours about 39 mg. That’s the reason we use 40 mg at bedtime as the low line on the cutoff clock. The bigger drink needed about 4.4 more hours, close to one half-life, because it was about twice the size.

Cups add up

An 8am coffee leaves only about 13 mg at 11pm on its own. But it doesn’t stay on its own. Three 8 oz coffees at 8am, noon and 4pm leave about 76 mg at 11pm, and 44 mg at 3am. Two 16 oz coffees at 7am and 11am, nearly 400 mg before lunch, still leave about 63 mg at 11pm.

That’s why the last cup and the total both count. The last cup sets most of what’s left, and the earlier ones raise the floor it sits on.

Why yours might not be 5 hours

Five hours is the middle of a wide spread. A 2024 review put the range in healthy adults at 1.5 to 9.5 hours. The same 3pm coffee leaves about 18 mg at 11pm on a 3 hour half-life and about 41 mg on 6. At the far ends it’s about 3 mg or 56 mg.

The things that move it most are known. The pill makes it about 1.5 times longer, the last month of pregnancy stretches it to about 10.5 hours, and heavy smoking makes it about a third shorter. What makes yours faster or slower has the studies and a chart of one coffee in four people.

Where the simple math stops

Heavy days last longer. In a 1990 study in San Francisco, 9 people had caffeine six times a day for 5 days. On 4.2 mg per kg a day, about 340 mg for a 180 lb person, the rate their bodies cleared it fell by about 40% compared with placebo, and it fell further on 12 mg per kg. The more you have in a day, the longer each cup lingers, so on a heavy day the 5 hour math is on the kind side.

The math also doesn’t know your cup. In a 2003 lab test the same coffee-shop drink, bought from the same shop on six days in a row, held anywhere from 259 to 564 mg. And it doesn’t know how strongly your receptors react to whatever is left.

Your turn

Put your own drinks and bedtime into the cutoff clock. If you’re on the pill, pregnant, a smoker or recently quit, set it on your half-life first. The quiz, Is my coffee keeping me up?, gives you the latest time for the drink you actually have.