What's my caffeine half-life?
About 5 hours on average, anywhere from 1.5 to 9.5 in healthy adults. Tap what's true for you and watch the same coffee race to your bedtime.
5hours for half, the average. A band of 3 to 6.
One 8 oz coffee at 2pm
- Left at 11:00pm, yours
- 30 mg
- Your 8 oz coffee cutoff
- 4:00pm
Pick what's true for you above. The clock and the other calculators use what you set here.
Fluvoxamine: in 8 people taking it, the half-life went from 5 to 31 hours. Most medicines don't change how fast you clear caffeine, but this one does. Ask your prescriber. No curve is drawn for it here.
Your genes (CYP1A2): the evidence is weak. A 2025 trial that tested the gene found no effect on sleep. Your own nights tell you more than a DNA report. Your genes and caffeine.
What your result means
- About 5 hours, the average: the usual cutoffs fit you. For an 11pm bedtime that's a 16 oz coffee by about 11am, an 8 oz by about 4pm.
- Longer, on the pill or pregnant: the same cup is still in you hours later, so move your last cup earlier or make it smaller. On the pill an 8 oz coffee needs to come by about 1:05pm for 11pm. In the last month of pregnancy, keep coffee to the morning.
- Shorter, as a smoker: caffeine leaves you faster. When you quit, the same coffee lasts about 1.5 times as long within 4 to 5 days, so cut it by about a third that week.
What to do next
- Check tonight's drinks on the cutoff clock. It uses the half-life you set here.
- Take fluvoxamine or another daily medicine? Ask your prescriber how it mixes with caffeine before you change anything (caffeine and antidepressants).
- Test it on your own nights for two weeks, since healthy adults run anywhere from 1.5 to 9.5 hours and no setting knows yours.
What moves it
| Who | Half-life used | 8 oz coffee at 2pm, left at 11pm | Its cutoff for 11pm | From |
|---|---|---|---|---|
| Typical adult | 5 hours | 30 mg | 4:00pm | Band 3 to 6, full range 1.5 to 9.5 (Antonio 2024, Gardiner 2025) |
| On a low-dose estrogen pill | 7.3 hours | 44 mg | 1:05pm | 7.88 hours against 5.37 in 9 matched women, so x 1.47 (Abernethy and Todd 1985) |
| Pregnant, last month | 10.5 hours | 55 mg | 9:10am | 10.5 hours in the last 4 weeks (Knutti 1982), up to about 13 (Parsons 1982) |
| Pregnant, earlier | 7.8 hours | 45 mg | 12:35pm | Somewhere from 5 to 10.5, since the rise starts early (Knutti 1982). The middle is drawn |
| Smoker, 20 or more a day | 3.2 hours | 16 mg | 6:15pm | Clearance fell 36% when 12 heavy smokers stopped, so x 0.64 (Faber and Fuhr 2004) |
One coffee at 2pm, four people
- A heavy smoker, 3.2 hours: 16 mg at 11pm
- Typical, 5 hours: 30 mg at 11pm
- On the pill, 7.3 hours: 44 mg at 11pm
- Late in pregnancy, 10.5 hours: 55 mg at 11pm
Quitting smoking
Within about 4 to 5 days of quitting, the same coffee lasts about 1.5 times as long as it did. That's why coffee can hit harder after you quit, and cutting it by about a third brings it back.
Medicines and genes
Most medicines don't change how fast you clear caffeine. Fluvoxamine does: in 8 people the half-life went from 5 to 31 hours. Ask your prescriber before mixing them. Gene tests for CYP1A2 are popular, but a 2025 trial that tested the gene found no effect on sleep, so your own nights tell you more. Your genes and caffeine has what a gene test can and can't tell you.
The pill and smoking factors each come from one study. When both apply, this page multiplies them, which is our arithmetic.
8 sources
- Antonio J and others, Common questions and misconceptions about caffeine supplementation: what does the scientific evidence really show? Journal of the International Society of Sports Nutrition, 2024doi.org
- Gardiner C and others, Dose and timing effects of caffeine on subsequent sleep: a randomized clinical crossover trial, Sleep, 2025doi.org
- Abernethy DR, Todd EL, Impairment of caffeine clearance by chronic use of low-dose oestrogen-containing oral contraceptives, European Journal of Clinical Pharmacology, 1985pubmed.ncbi.nlm.nih.gov
- Knutti R, Rothweiler H, Schlatter C, The effect of pregnancy on the pharmacokinetics of caffeine, Archives of Toxicology Supplement, 1982pubmed.ncbi.nlm.nih.gov
- Parsons WD, Pelletier JG, Delayed elimination of caffeine by women in the last 2 weeks of pregnancy, Canadian Medical Association Journal, 1982pubmed.ncbi.nlm.nih.gov
- Faber MS, Fuhr U, Time response of cytochrome P450 1A2 activity on cessation of heavy smoking, Clinical Pharmacology and Therapeutics, 2004pubmed.ncbi.nlm.nih.gov
- Jeppesen U and others, A fluvoxamine-caffeine interaction study, Pharmacogenetics, 1996pubmed.ncbi.nlm.nih.gov
- Grzegorzewski J and others, Pharmacokinetics of Caffeine: A Systematic Analysis of Reported Data, Frontiers in Pharmacology, 2021doi.org
