How much caffeine is in your system right now?
Log what you drank and when. CaffeineCal models your level hour by hour using caffeine's half-life, and shows what is still circulating at bedtime.
How much caffeine is in common drinks?
These are the averages the calculator uses. Real cups vary a lot, brewed coffee alone spans roughly 70 to 140 mg depending on bean, roast, grind and brew time, and coffee-shop servings routinely run larger than the listed size.
| Drink | Serving | Caffeine |
|---|---|---|
| Brewed drip coffee | 8 oz | 95 mg |
| Cold brew | 8 oz | 100 mg |
| Espresso | 1 shot (1 oz) | 63 mg |
| Latte / cappuccino | 1 shot | 63 mg |
| Americano (double) | 2 shots | 126 mg |
| Instant coffee | 8 oz | 62 mg |
| Decaf coffee | 8 oz | 2 mg |
| Black tea | 8 oz | 47 mg |
| Green tea | 8 oz | 28 mg |
| Matcha | 8 oz | 70 mg |
| Yerba mate | 8 oz | 85 mg |
| Energy drink | 8.4 oz can | 80 mg |
| Energy drink, large | 16 oz can | 160 mg |
| Energy shot | 2 oz | 200 mg |
| Cola | 12 oz can | 34 mg |
| Diet cola | 12 oz can | 46 mg |
| Dark chocolate | 1 oz | 12 mg |
| Caffeine pill | 1 tablet | 200 mg |
Sources: FDA consumer guidance and USDA food data averages. Individual products differ; check the label when one exists.
How the calculator works
Caffeine leaves your body by first-order elimination: a roughly constant fraction is cleared per hour, which is what "half-life" describes. With the average adult half-life of about 5 hours, half of a dose is gone in 5 hours, three quarters in 10 hours, and about 88 percent in 15 hours. Each drink you log is absorbed over about 45 minutes, then decays on that schedule, and the tool sums every drink's curve into the line above.
Where it is honest to be rough: half-life is not one number. Published values in healthy adults run from about 1.5 to 9.5 hours. Variants of the CYP1A2 liver enzyme explain much of the spread, smoking roughly doubles clearance speed, and pregnancy or oral contraceptives slow it substantially, in late pregnancy the half-life can exceed 15 hours. The fast, average and slow settings approximate this, but if you consistently sleep fine after an evening espresso, or lie awake after a lunchtime cup, believe your own experience over the preset.
When should you stop drinking caffeine?
The most cited experiment on caffeine timing is a 2013 randomized, double-blind trial by Drake and colleagues in the Journal of Clinical Sleep Medicine. Participants took 400 mg of caffeine, roughly a large cold brew, at bedtime, 3 hours before bed, or 6 hours before bed, while a device measured their actual sleep. Even the dose taken 6 hours out cut measured sleep by over an hour. The uncomfortable detail: people largely did not report their sleep as worse, the loss was invisible to them.
The practical translation is a cutoff at least 6 to 8 hours before bed for meaningful doses, earlier if you metabolize slowly or your doses are large. There is no bright line where remaining caffeine becomes harmless, which is why this tool draws a low reference line at 50 mg, about half a cup, rather than promising a safe number.
Frequently asked questions
The average elimination half-life is about 5 hours: half the dose gone in 5 hours, half of the remainder in the next 5. Caffeine from a large afternoon dose is still detectable well past midnight. The individual range is wide, about 1.5 to 9.5 hours, set mostly by CYP1A2 genetics, smoking, pregnancy, medications and liver function. At the 5 hour average, a 95 mg cup at noon leaves roughly 26 mg at 10 pm.
The Drake 2013 trial found 400 mg taken even 6 hours before bed cut measured sleep by more than an hour, mostly without people noticing. A last-caffeine cutoff of 6 to 8 hours before bedtime is the common evidence-based recommendation, with slow metabolizers stopping earlier. Set your bedtime above and the calculator shows your estimated level directly.
The FDA cites 400 mg a day, four to five cups of coffee, as not generally associated with dangerous effects in healthy adults. It is guidance, not a personal guarantee. Heart conditions, anxiety, reflux and several medications lower the sensible number, and ACOG advises under 200 mg daily during pregnancy. When in doubt, that is a doctor conversation, not a calculator's call.
An 8 oz cup of drip coffee averages about 95 mg, with a real range of roughly 70 to 140 mg. Espresso is about 63 mg per shot. A 16 oz shop cold brew often tops 200 mg. Black tea runs about 47 mg, green tea 28 mg, cola 34 mg per can, and energy drinks 80 mg per small can or 160 mg and up for large ones.
Yes, about 2 to 7 mg per cup, versus roughly 95 mg for regular. Trivial for most people, but several evening decafs add up, and very sensitive people can still feel it.
Mostly the CYP1A2 liver enzyme, which has common genetic variants that make caffeine clearance faster or slower. Smoking speeds clearance roughly twofold; pregnancy and oral contraceptives slow it, with late-pregnancy half-life sometimes beyond 15 hours. Adenosine receptor genetics also shape how strongly the same blood level is felt. The fast, average and slow presets here are a rough map of that territory.
Sources
- Drake C, Roehrs T, Shambroom J, Roth T. Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed. Journal of Clinical Sleep Medicine, 2013. The randomized trial behind the 6-hour cutoff guidance.
- US FDA: Spilling the Beans, How Much Caffeine Is Too Much? Source of the 400 mg daily guidance and typical beverage caffeine figures.
- American College of Obstetricians and Gynecologists: caffeine in pregnancy. Source of the under-200 mg pregnancy guidance.
- StatPearls: Caffeine. Pharmacokinetics reference for the half-life range and CYP1A2 metabolism.