Caffeine calculator: how much is still in you at bedtime?

Caffeine’s half-life averages about five hours, so half of your afternoon coffee is still working when dinner is done. A 300 mL flat white at 3pm can leave around 80 mg in your system at 10pm. Add your drinks below to see your own curve.

Georgina Waugh, Clinical Nutritionist

Reviewed by Georgina Waugh, Clinical Nutritionist. Updated 13 September 2026.

Work out my caffeine

An estimate for healthy adults, not medical advice. If you are pregnant, breastfeeding or on medication, ask your GP or pharmacist how caffeine fits.

Your caffeine day

We have started you with a flat white at 7:30am and another at 3pm. Change them to your own day: amounts are Australian averages, so adjust the mg if your label or café says otherwise.

The calculator needs JavaScript switched on. The table further down shows what is likely left at 10pm for the most common drinks.

What you drank

    Faster, 3 hoursAverage, 5Slower, 9

    Half-life: 5 hours

    Likely still in your system at 10pm

    0 mg

    Add a drink to see your curve

    Dots on the baseline are your drinks. The dashed line is the amount EFSA notes can affect sleep in some people when taken close to bed, a reference rather than a cut-off.

    The curve assumes each drink is fully absorbed within about 45 minutes and then clears at the half-life you set. Real bodies are messier, so read it as a rough guide.

    How much caffeine is in your drink?

    These are the amounts the calculator starts from, and what is likely left at 10pm at an average five-hour half-life.

    DrinkCaffeine per serveLeft at 10pm if drunk at 12pmAt 3pmAt 5pm
    Flat white, latte or cappuccino300 mLabout 200 mg50 mg80 mg100 mg
    Espresso or long blackone café espresso serveabout 107 mg25 mg40 mg55 mg
    Instant coffee300 mLabout 100 mg25 mg40 mg50 mg
    Black tea300 mLabout 57 mg15 mg20 mg30 mg
    Energy drink250 mL canabout 80 mg20 mg30 mg40 mg
    Energy drink500 mL canabout 160 mg40 mg60 mg80 mg
    Cola375 mL can, at mostabout 55 mg15 mg20 mg30 mg

    Coffee, tea and energy drink amounts are worked out from FSANZ’s 2025 caffeine review. The espresso figure is the average from a Gold Coast study of 97 café espressos, where serves ranged from 25 to 214 mg. Cola is the most the Food Standards Code allows; many colas contain less.

    How long does caffeine last?

    Caffeine is almost fully absorbed within about 45 minutes of drinking it. After that, your liver clears it steadily, and the usual way to describe the speed is its half-life: the time it takes for half of it to go.

    In healthy adults, that half-life averages about five hours, according to the Institute of Medicine’s review of caffeine pharmacology, but it ranges from roughly 1.5 to 9.5 hours. That spread matters. With a three-hour half-life, the 3pm flat white leaves about 40 mg at 10pm. With a nine-hour half-life, it leaves about 120 mg.

    Why a 3pm coffee can still matter at night

    In a 2013 sleep study, 12 healthy adults took 400 mg of caffeine at bedtime, three hours before bed or six hours before bed, and slept at home with a sleep monitor. All three timings disturbed sleep compared with a placebo. Even at six hours, measured sleep dropped by more than an hour, while people’s own sleep diaries did not show a clear difference.

    That was a large dose, so it does not mean one small coffee after lunch will cost you an hour of sleep. It does mean that how you feel about your afternoon coffee is not a reliable guide to what it is doing overnight. The European Food Safety Authority puts the sleep-sensitive amount lower still: around 100 mg can affect sleep in some adults when taken close to bedtime.

    Why your number might be different

    • The contraceptive pill. Oral contraceptive use can double caffeine’s half-life, and a review of 141 studies found the same slowing across a wide range of doses.
    • Pregnancy. Caffeine clears more slowly, and EFSA’s guidance is up to 200 mg a day. The calculator does not model pregnancy, so talk to your GP or midwife.
    • Smoking. Smoking speeds caffeine clearance, and stopping brings it back to non-smoking rates, which can make the same coffee feel stronger.
    • Your genes and your medicines. One liver enzyme, CYP1A2, does most of the work, and how active it is varies from person to person. Some medicines slow it down, so ask your pharmacist if you are unsure.

    What I ask about first. Not how many coffees you have. I want to know when the last one is, and what it is doing for you.

    A 3pm coffee that gets you through a slump is information. So is waking at 3am, or needing the first cup before you can talk to anyone. Caffeine is often covering for something, and the useful question is what.

    If you try moving your last coffee earlier for two weeks, keep a note of how you sleep and how the afternoons feel. That is more useful than any number on a chart.

    When to talk to your GP

    Book in with your GP if

    • you have had trouble getting to sleep or staying asleep for more than a few weeks
    • you are relying on caffeine to get through most days, or feel unwell when you go without
    • caffeine gives you a racing or irregular heartbeat, chest discomfort, or anxiety that will not settle
    • you are pregnant, breastfeeding, or taking medication and are not sure how caffeine fits

    Caffeine research is about averages. Healthdirect has a plain-language page on insomnia and when to get help.

    If tiredness is what keeps sending you back to the kettle, our page on how we work with fatigue and brain fog sets out where we start, and mood, stress and sleep covers the sleep side. For more on the morning cup, read whether coffee on an empty stomach is a problem.

    Tired enough to need the 3pm coffee?

    Bring your caffeine curve, your usual sleep, and when the energy dips. A short call is usually enough to work out whether the answer is your routine, a conversation with your GP, or a closer look at what is behind the fatigue. No test is booked on the call.

    Book a free 15-minute call

    Fifteen minutes on the phone with a clinical nutritionist, at no cost.

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    Andrew, Google review · 5.0 on Google

    Common questions about caffeine

    How long does caffeine stay in your system?

    Caffeine’s half-life averages about five hours in healthy adults, but ranges from about 1.5 to 9.5 hours. So roughly half of a coffee is still circulating five hours later, and a quarter after ten. A 300 mL flat white at 3pm can leave around 80 mg in your system at 10pm.

    How much caffeine is in a flat white?

    Food Standards Australia New Zealand’s figures work out to about 200 mg for a 300 mL flat white, latte or cappuccino. Café coffee varies a lot: in one Gold Coast study, single espresso serves ranged from 25 to 214 mg, so use any number as a starting point.

    What time should I stop drinking coffee?

    There is no single cut-off, because people clear caffeine at very different speeds. In one sleep study, a large dose taken six hours before bed still reduced measured sleep by more than an hour, even though people did not notice it. Try your usual day in the calculator and see what is left at your bedtime.

    Does the contraceptive pill make caffeine last longer?

    It can. Oral contraceptive use can double caffeine’s half-life, which is why the calculator has a checkbox for it. With a doubled half-life, that 3pm flat white could leave around 125 mg at 10pm instead of 80.

    How much caffeine is too much?

    The European Food Safety Authority considers up to 400 mg a day, and single doses up to 200 mg, safe for healthy adults, and up to 200 mg a day during pregnancy. Separately, it notes that around 100 mg can affect sleep in some people when taken close to bedtime.

    Sources

    1. Institute of Medicine (US) Committee on Military Nutrition Research. Pharmacology of caffeine. In: Caffeine for the Sustainment of Mental Task Performance. National Academies Press, 2001. Caffeine is almost fully absorbed within 45 minutes; the half-life averages about 5 hours and ranges from 1.5 to 9.5 hours; oral contraceptives can double it and smoking speeds clearance.
    2. 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;9(11):1195-200. 400 mg of caffeine taken at bedtime, 3 hours or 6 hours before bed, in 12 healthy adults sleeping at home.
    3. EFSA Panel on Dietetic Products, Nutrition and Allergies. Scientific Opinion on the safety of caffeine. EFSA Journal, 2015;13(5):4102. Single doses up to 200 mg and up to 400 mg a day raise no safety concerns for healthy adults; up to 200 mg a day in pregnancy; around 100 mg may affect sleep in some adults close to bedtime.
    4. Food Standards Australia New Zealand. P1056 Caffeine Review, Supporting Document 2: Dietary intake assessment. 2025. 400 mg is roughly two 300 mL flat whites, lattes or cappuccinos, four 300 mL instant coffees, five 250 mL energy drinks or seven 300 mL black teas, from the Australian Food Composition Database. The Food Standards Code caps energy drinks at 320 mg per litre and cola at 145 mg per kg.
    5. Desbrow B, Hughes R, Leveritt M, Scheelings P. An examination of consumer exposure to caffeine from retail coffee outlets. Food and Chemical Toxicology, 2007;45(9):1588-92. 97 espressos bought on the Gold Coast averaged 106 mg per serve, ranging from 25 to 214 mg.
    6. 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. Data from 141 studies: smoking shortens caffeine’s half-life and oral contraceptive use lengthens it, across a wide range of doses.

    Important: This calculator gives a general estimate for healthy adults, reviewed by a clinical nutritionist. It is not medical advice and does not replace care from your GP, pharmacist or another qualified health professional. Read our full disclaimer.

    Georgina Waugh, Clinical Nutritionist at Wellbeing George

    Reviewed by Georgina Waugh

    Clinical Nutritionist, BHSc Nutritional Medicine

    Last updated: 13 September 2026

    Sources reviewed: the Institute of Medicine’s review of caffeine pharmacology, EFSA’s safety opinion, FSANZ’s 2025 caffeine review and published sleep research