Is the half-life of caffeine the same for everyone?

No. 3 to 6 hours is the usual adult range, but measured values run from about 2 hours to well over 10, depending on genes, smoking, hormones, pregnancy, liver health and medication.

What is the half-life of caffeine during pregnancy?

It rises from early pregnancy onward. One study measured an average of 3 hours in non-pregnant women and 10.5 hours in the last four weeks of pregnancy, and another found values of up to 16 hours in pregnant women. See caffeine during pregnancy.

How many half-lives until caffeine is gone?

After five half-lives about 3 % is left, which is usually treated as cleared. At a 5-hour half-life that is about 25 hours. See how long caffeine lasts for a cup of coffee hour by hour.

What is the half-life of caffeine?

By the Caffeine Clock team · Updated September 2026

Caffeine's half-life is the time your body takes to clear half of the caffeine in it, and for most adults it is 3 to 6 hours. Smoking shortens it, while oral contraceptives, pregnancy and liver disease lengthen it, so yours can fall well outside that range.

Half-life 5 h · Sleep threshold 100 mg · Bedtime 22:00

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What half-life means

Your body does not remove a fixed number of milligrams per hour. It clears caffeine in proportion to how much is there, so the amount halves over the same stretch of time again and again. With a 5-hour half-life, 100 mg becomes 50 mg after 5 hours, 25 mg after 10 hours and about 12 mg after 15 hours.

This is also why a second coffee stacks on top of what is left of the first. The calculator adds up every drink's curve and uses your half-life for all of them; the methodology shows the formula.

How much is left, by half-life

The table starts from 100 mg that has already been absorbed, so it shows elimination alone. Real drinks also take 30 to 120 minutes to peak, which the calculator above includes.

Caffeine left from 100 mg, by hours since it was absorbed
Hours later	3-hour half-life	5-hour half-life	6-hour half-life	10.5-hour half-life
3	50 mg	66 mg	71 mg	82 mg
6	25 mg	44 mg	50 mg	67 mg
9	13 mg	29 mg	35 mg	55 mg
12	6 mg	19 mg	25 mg	45 mg
24	under 1 mg	4 mg	6 mg	21 mg

The last column is the average half-life measured in the final four weeks of pregnancy in one study. At that pace, a fifth of a morning coffee is still in your body the next morning.

What changes your half-life

About 95 % of caffeine is cleared by one liver enzyme, CYP1A2. Its activity varies five- to six-fold between people, and twin studies trace most of that difference to genes.

Smoking speeds up caffeine clearance and shortens the half-life. Oral contraceptives slow clearance and lengthen it. Pregnancy lengthens it the most: from about 3 hours to 10.5 hours on average by the last month in one study, with the rise starting early in pregnancy and values back to normal within about a month after delivery in most women. Liver disease such as cirrhosis slows clearance, and some medicines block it, including the antidepressant fluvoxamine and the antibiotics norfloxacin and pipemidic acid.

Finding your own half-life

There is no home test. In studies, half-life is measured from saliva or blood samples taken several hours apart after a known dose of caffeine. For everyday use, start from the default of 5 hours, try a shorter value if you smoke or a longer one if you take the pill or are pregnant, and see which one matches how you actually sleep.

Set it under Change in the calculator above. The curve, the amount left at bedtime and the time you drop below your threshold all follow it.

Frequently asked questions

: No. 3 to 6 hours is the usual adult range, but measured values run from about 2 hours to well over 10, depending on genes, smoking, hormones, pregnancy, liver health and medication.
: It rises from early pregnancy onward. One study measured an average of 3 hours in non-pregnant women and 10.5 hours in the last four weeks of pregnancy, and another found values of up to 16 hours in pregnant women. See caffeine during pregnancy.
: After five half-lives about 3 % is left, which is usually treated as cleared. At a 5-hour half-life that is about 25 hours. See how long caffeine lasts for a cup of coffee hour by hour.

More about caffeine

Sources

Mort JR, Kruse HR. Timing of blood pressure measurement related to caffeine consumption. Annals of Pharmacotherapy. 2008;42(1):105-110. https://doi.org/10.1345/aph.1k337
Grzegorzewski J, Bartsch F, Köller A, König M. Pharmacokinetics of caffeine: a systematic analysis of reported data for application in metabolic phenotyping and liver function testing. Frontiers in Pharmacology. 2021;12:752826. https://doi.org/10.3389/fphar.2021.752826
Knutti R, Rothweiler H, Schlatter C. Effect of pregnancy on the pharmacokinetics of caffeine. European Journal of Clinical Pharmacology. 1981;21(2):121-126. https://doi.org/10.1007/BF00637512
Knutti R, Rothweiler H, Schlatter C. The effect of pregnancy on the pharmacokinetics of caffeine. Archives of Toxicology Supplement. 1982;5:187-192. https://doi.org/10.1007/978-3-642-68511-8_33