Do babies and children clear caffeine at the same speed as adults?

Newborns clear caffeine very slowly, and premature babies most slowly of all: StatPearls on NIH's NCBI Bookshelf cites half-lives of up to 100 hours in premature infants. Sources differ slightly on when this catches up. NIH's LactMed database says caffeine clearance reaches adult values by 3 to 5 months of age, while StatPearls says children older than 9 months have half-lives similar to adults.

Does drinking caffeine every day change how long it lasts?

Not in terms of how fast your body clears it. A National Academies report found that in healthy people, repeated caffeine intake does not change how caffeine is absorbed or broken down. The report also says tolerance to some of caffeine's effects develops with continued use, so you may notice it less even though it stays in your body just as long.

I fall asleep fine after an afternoon coffee. Is it still affecting my sleep?

It may be. In the 2013 study that gave people caffeine 6 hours before bed, a sleep monitor picked up disrupted sleep but the participants' own sleep diaries did not. A 2025 trial likewise found a gap between measured and self-rated sleep, and its authors concluded that people may have trouble judging how caffeine affects their sleep.

Is decaf okay in the evening?

Decaf still has a little caffeine: the FDA says decaf coffee typically has 2 to 15 mg in an 8-ounce cup. That is well below the 100 mg single dose that EFSA says may affect sleep in some adults, and below the 100 mg dose that showed no significant sleep effect even 4 hours before bed in a 2025 trial. If you're very sensitive, several cups still add up.

How Long Does Caffeine Last?

Caffeine reaches its peak level in your blood within about an hour, and you may feel its effects for 4 to 6 hours (MedlinePlus). It stays in your body much longer than that. In healthy people the average half-life, the time it takes to clear half of a dose, is about 5 hours, but it can be anywhere from 1.5 to 9.5 hours (National Academies). So half of an afternoon coffee can still be in your system at dinner, and enough to disturb sleep can be left at bedtime. Sleep studies support stopping caffeine at least 6 hours before bed, and longer for big doses (Drake et al., 2013).

How caffeine moves through your body

Caffeine is absorbed quickly and almost completely, with about 99 percent absorbed within 45 minutes. Blood levels peak anywhere from 15 to 120 minutes after you drink it, depending partly on how fast your stomach empties and what else you’ve eaten (National Academies). Your liver then breaks it down, mainly with an enzyme called CYP1A2 (StatPearls). Anything that speeds up or slows down that enzyme changes how long caffeine lasts.

Here’s what a 5-hour half-life would mean for a 200 mg coffee at noon. The numbers are worked out from the average half-life, so your own body could clear it faster or slower.

Time	Caffeine left (5-hour half-life)
12 p.m.	200 mg
5 p.m.	100 mg
10 p.m.	50 mg
3 a.m.	25 mg

What makes caffeine last longer or shorter

The wide range in half-life comes from natural differences between people and from things like pregnancy, obesity, birth control pills, smoking and altitude (National Academies). These are the factors with the clearest numbers.

Pregnancy

Caffeine’s half-life can stretch to as long as 15 hours during pregnancy, especially in the last trimester (StatPearls). It returns to normal within the first week after giving birth (LactMed). Pregnancy also has a lower daily limit. Our guide on how much caffeine is too much covers it, and your provider can advise you.

Smoking

Smoking speeds up caffeine metabolism. In smokers, the half-life is up to 50 percent shorter than in nonsmokers (StatPearls). When someone quits, caffeine clearance goes back to nonsmoking levels (National Academies), so the same coffee will stay in their body longer than it used to.

Birth control pills and estrogen

Studies of oral contraceptives found they can double caffeine’s half-life. Those studies are older, and the effect of newer pills hasn’t been studied. Estrogen replacement therapy may also slow caffeine metabolism in postmenopausal women (National Academies).

Medications

Drugs that block the liver enzymes that clear caffeine make its half-life longer (StatPearls). The antidepressant fluvoxamine is a strong example. In a small study of seven healthy adults, it lengthened caffeine’s average half-life from 4.9 hours to 56 hours (Culm-Merdek et al., 2005). The FDA notes that some medications can make people more sensitive to caffeine (FDA). If you take a prescription medicine, ask your doctor or pharmacist whether caffeine interacts with it.

Liver disease

Because the liver does most of the work, liver disease also lengthens caffeine’s half-life. People with advanced cirrhosis may get insomnia, nervousness and headaches from amounts of caffeine that people without liver disease usually handle well (StatPearls). If you have liver disease, talk to your doctor about how much caffeine is safe for you.

How caffeine affects sleep

The best-known study on timing came out in 2013. Twelve healthy sleepers took 400 mg of caffeine at bedtime, 3 hours before bed, or 6 hours before bed, and on another night took a placebo. All three caffeine times disrupted sleep. Even at 6 hours, caffeine cut total sleep by more than an hour, as measured by a home sleep monitor. The authors said the results support the advice to avoid substantial caffeine for at least 6 hours before bedtime, and that people should stop afternoon caffeine before 5 p.m. at the very least (Drake et al., 2013).

A 2023 meta-analysis pooled 24 studies. On average, caffeine cut total sleep by 45 minutes and sleep efficiency by 7 percent. It added 9 minutes to the time needed to fall asleep and 12 minutes of time awake during the night, and it reduced deep sleep. To avoid losing sleep, the authors estimated that a coffee (107 mg per 250 mL, a little over 8 ounces) should be drunk at least 8.8 hours before bed. For a standard pre-workout serving of 217.5 mg, the gap rises to at least 13.2 hours (Gardiner et al., 2023).

A 2025 trial by the same lead author tested dose and timing directly in 23 young men who normally had moderate amounts of caffeine. A 100 mg dose had no significant effect on sleep when taken 12, 8 or even 4 hours before bed. A 400 mg dose within 12 hours of bedtime delayed sleep and changed sleep structure, and within 8 hours it also made sleep more broken. The authors concluded that 100 mg can be taken up to 4 hours before bed, but a single 400 mg dose may harm sleep anywhere within 12 hours (Gardiner et al., 2025).

The two Gardiner papers disagree about a regular coffee. The 2023 meta-analysis says to stop about 8.8 hours before bed, and the 2025 trial found 100 mg harmless at 4 hours. The trial is newer and tested timing directly, but it involved only 23 young men. The meta-analysis is older but pools many more studies of different designs. EFSA, the European Food Safety Authority, takes a cautious line: a single 100 mg dose may affect sleep in some adults, particularly close to bedtime (EFSA).

When to stop caffeine before bed

Putting the research together:

For any substantial amount, stop at least 6 hours before bed. That’s the minimum the 2013 study supports (Drake et al., 2013). For a 10:30 p.m. bedtime, that means nothing after 4:30 p.m.
For large doses, such as a 217.5 mg pre-workout serving or 400 mg at once, allow 12 to 13 hours, based on the 400 mg trial results and the 13.2-hour estimate for pre-workouts (Gardiner et al., 2025; Gardiner et al., 2023). With a 10:30 p.m. bedtime, 13.2 hours means taking a pre-workout by about 9:15 a.m., so evening training sessions are better without one.
If caffeine stays in your body longer because of pregnancy, birth control pills, a medication or liver disease, set an earlier cutoff. The figures above come from studies of healthy adults.

Two coffees taken hours apart overlap in your body, which is one reason to keep your daily total within the limits for your situation.