What is the half-life of caffeine?

The half-life of caffeine is about 5 hours in a healthy adult: half of the caffeine you drink is gone after about 5 hours, and a quarter is still there after about 10.

What a 5-hour half-life means

Half-life is the time it takes your body to clear half of the caffeine that is in it. It works the same way however much is there: after one half-life, half is left; after two, a quarter; after three, an eighth. So a 200 mg drink at noon still leaves about 50 mg at 10 pm for an average adult, which is right at the level where sleep starts to suffer.

Caffeine is absorbed over the first 30 to 60 minutes, so real levels rise for a while before the half-life takes over. The tables below show only the clearance part, from a starting amount.

How much is left, hour by hour

Hours later	100 mg, 5 h half-life	200 mg, 3 h	200 mg, 5 h	200 mg, 7 h
0	100 mg	200 mg	200 mg	200 mg
2	76 mg	126 mg	152 mg	164 mg
4	57 mg	79 mg	115 mg	135 mg
5	50 mg	63 mg	100 mg	122 mg
6	44 mg	50 mg	87 mg	110 mg
8	33 mg	31 mg	66 mg	91 mg
10	25 mg	20 mg	50 mg	74 mg
12	19 mg	13 mg	38 mg	61 mg
15	13 mg	6.3 mg	25 mg	45 mg
20	6.3 mg	2 mg	13 mg	28 mg

Between a fast and a slow clearer the gap is large: ten hours after 200 mg, a 3-hour half-life leaves about 20 mg and a 7-hour half-life leaves about 74 mg.

What makes it faster or slower

Smoking or vaping nicotine daily: about 40% shorter. Studies report about 3.5 h vs 6 h.
Hormonal birth control with estrogen: about 90% longer. Reported to roughly double it.
Pregnancy: about 100% longer. Slower clearance that grows through pregnancy; estimate.
Alcohol the same evening: about 15% longer. Alcohol slows clearance; estimate.
Genes: a common variant of the CYP1A2 enzyme makes some people slow metabolisers; they feel coffee for longer.
Liver disease and some medicines (for example fluvoxamine and some antibiotics) can make it much longer. Ask your doctor or pharmacist.

The main CaffeineIQ check lets you set these, or enter your own half-life if you know it.

FAQ

What is the half-life of caffeine?

About 5 hours for a healthy adult, with a normal range of roughly 3 to 7 hours.

Does smoking change the half-life of caffeine?

Yes. Smoking speeds up the liver enzyme that breaks caffeine down; studies report a half-life of around 3 to 3.5 hours in smokers.

Why is caffeine half-life longer in pregnancy?

Pregnancy slows the enzyme that clears caffeine, more so in later months, so the half-life can roughly double.

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Estimates, not medical advice. How it works.