Your caffeine, hour by hour.
Tap the drinks you had today with their times, set your bedtime, and the tool draws the caffeine still in your body from 06:00 to 06:00 using a half-life of 4, 5 or 7 hours. You get the milligrams left at bedtime, the time you drop under 50 mg, your daily total against the 400 mg guidance, one sentence of advice, and a card to save or share.
Add your drinks, set your bedtime.
Set a time, tap a drink, and it lands on your day. The curve shows how much caffeine is still in your body, hour by hour, from 06:00 to 06:00 the next morning.
Drinks, caffeine per typical serving
Your day
Example dayNothing added yet. Set a time above, tap a drink, and it appears here.
Caffeine in your body
The 50 mg line is about half a mug of filter coffee: a practical marker for bedtime, not an official limit. The curve is an estimate with average serving sizes and the half-life you chose.
No drinks on the clock yet.
Tap a drink card above and the curve starts. Or load a typical office day, four drinks between 08:00 and 16:30, to see how the clock works.
How it works.
- Set the time of a drink, then tap its card: espresso, filter coffee, tea, cola, energy drink, decaf or chocolate. Each drink keeps its own time in the list, where you can edit or remove it.
- Enter your bedtime and pick a half-life: 5 hours for most adults, 7 hours with oral contraceptives or in pregnancy, 4 hours if you clear caffeine fast.
- Read the curve and the result: milligrams at bedtime against the 50 mg line, the time you drop under it, the day's total against 400 mg, and one sentence on what to move. Then save or share the card.
Where the 5 hour half-life comes from
Caffeine leaves the body by first-order decay: in each half-life the amount falls by half. In healthy adults that half-life averages about 5 hours, with a range of roughly 1.5 to 9.5 hours depending on genes, liver enzymes and habits. Oral contraceptives and pregnancy roughly double it, so a 95 mg mug at 15:00 that leaves 31 mg at 23:00 on a 5 hour clock leaves 55 mg on a 10 hour one. Smoking shortens it. The tool lets you choose 4, 5 or 7 hours and draws every drink as its own decaying curve, added together from 06:00 to 06:00, starting the day at 0 mg. The guide on when the last cup should be goes through the evidence.
What the 50 mg line and the 400 mg guidance mean
The European Food Safety Authority concluded in 2015 that up to 400 mg of caffeine a day raises no safety concern for healthy adults, that single doses of up to 200 mg are fine, and that pregnancy calls for a lower ceiling of 200 mg a day. Typical servings vary: a 240 ml mug of filter coffee carries around 80 to 100 mg, a 30 ml espresso 60 to 65 mg, a cup of black tea 40 to 50 mg and green tea about 28 mg. The 50 mg line at bedtime is a practical marker rather than an official limit: about half a filter coffee, a level most people can fall asleep on. In a 2013 study by Drake and colleagues, 400 mg of caffeine taken 6 hours before bed cut sleep measured at home by about 1 hour, although the participants did not feel it. Sensitive sleepers and anyone short of their 7 to 9 hours do well with a cut-off of 8 to 10 hours before bed; for a 23:00 bedtime that is the last coffee by 13:00 to 15:00. Your chronotype shifts the picture: a late type in bed at 01:00 has 2 more hours of clearance than an early type at 23:00.
What this tool is not
The clock is a simple exponential model with average caffeine contents. A real espresso can range from 40 to 120 mg depending on bean, roast and machine, and individual clearance varies more than fourfold. It cannot see your genes, your liver or your medicines, and it does not diagnose anything. If caffeine gives you palpitations, anxiety or a racing heart, or you have a heart condition, talk to a doctor rather than a calculator. Caffeine is one evening lever: screens in the evening and an irregular bedtime move sleep at least as much as a late tea does.
Frequently asked.
Does decaf really count?
A 240 ml mug of decaf carries about 3 mg, which is why the card shows 3 mg. Three mugs after dinner add less than 10 mg, far under the 50 mg line, so decaf is the evening option for most people.
Why does the curve start at 0 mg at 06:00?
The model counts one day at a time. If you went to bed with 60 mg the night before, around 23 mg would be left at 06:00 on a 5 hour clock and about 10 mg by noon, small enough to leave out. The first drink of the day dominates from there.
How accurate are the milligram figures on the cards?
They are typical values from food composition tables: filter coffee 95 mg per 240 ml, espresso 63 mg per 30 ml shot, black tea 47 mg, energy drink 80 mg per 250 ml can. Real cups vary by bean, roast and brewing time, so treat the curve as an estimate with a margin of perhaps 30 percent.
Which half-life should I pick?
5 hours fits most healthy adults. Choose 7 hours if you take oral contraceptives, are pregnant, or notice that an afternoon coffee keeps you awake; 4 hours if you smoke or clear caffeine visibly fast. The guide on caffeine timing explains the genetics behind the spread.
Is 400 mg a day a target?
No, a ceiling. The 2015 EFSA opinion puts the level at which healthy adults show no safety concern at 400 mg a day, or 200 mg in pregnancy, with single doses of up to 200 mg. Less is fine, and the tool flags a day that passes the figure you chose.
What does the tool save?
Your drinks with their times, your bedtime, the half-life and the guidance you chose, stored in your own browser so the clock shows your day next time. Nothing is sent anywhere.
Guides behind this tool
Life
Caffeine: when the last cup should be
Health
How much sleep adults really need: 7 to 9 hours, and why
Life
Early bird or night owl: what your chronotype means
Life
Screens in the evening and sleep: what the studies foundMore tools
This clock is a simple exponential estimate built on average caffeine contents and a half-life you choose; it is not a measurement, a diagnosis or medical advice, and it cannot account for your genes, medicines, pregnancy, heart conditions or anxiety. If caffeine gives you palpitations, anxiety or poor sleep, talk to a doctor. This page is for general information and does not replace medical advice.