How much caffeine are you having — and how much is left at bedtime?
This caffeine calculator adds up the caffeine in your coffee, tea, soft drinks and energy drinks, compares the total with the daily amounts food-safety authorities consider of no concern, and estimates how much caffeine is still in your body at bedtime. A chart shows the level rising with each drink and fading through the day.
It works by weight too: for under-18s the guide is 3 mg per kg of body weight, and every result shows your mg per kg. Choose the pregnancy setting for the lower 200 mg guide, and lengthen the half-life if you know you clear caffeine slowly.
How to use the caffeine calculator
- Choose Adult, Pregnant or breastfeeding or Under 18, and enter your body weight.
- For each drink, pick it from the list (or choose Other and type the mg from the label) and set the time you had it.
- Set your bedtime and, if you like, a different half-life.
- Read your total against the guide, the caffeine left at bedtime, when it falls below 100 mg, and the chart.
Caffeine Calculator features
Daily total against the guides
400 mg for healthy adults, 200 mg in pregnancy and breastfeeding, 3 mg/kg for under-18s.
Caffeine left at bedtime
A half-life model estimates what is still in your body when you go to sleep.
By weight
Shows mg per kg and flags a single drink above the single-dose guide.
Drink presets
FDA and EFSA example amounts for coffee, espresso, tea, cola and energy drinks, all editable.
How the caffeine calculator works
Caffeine is absorbed quickly and removed at a steady proportion per hour, so the amount left halves every half-life. The calculator adds each drink and applies amount left = dose × 0.5hours since ÷ half-life, treating each drink as absorbed at once.
Example: 200 mg at 08:00 and 100 mg at 14:00 with a 5-hour half-life leaves 200 × 0.514 ÷ 5 + 100 × 0.58 ÷ 5 ≈ 29 + 33 = 62 mg at 22:00. The level drops below 100 mg at about 18:30.
Food Standards Australia New Zealand’s 2022 caffeine safety assessment (Proposal P1056) gives a usual adult half-life of 3–7 hours, rising to about 10 hours by 17 weeks of pregnancy and up to 18 hours by the end. Starting oral contraceptives, quitting smoking and some medicines also change how fast it is cleared.
Caffeine guides (checked 24 October 2026)
| Who | Guide | Source |
|---|---|---|
| Healthy adults | Up to 400 mg a day (about 5.7 mg/kg); single doses up to 200 mg | EFSA 2015; FDA (page current as of 28 Aug 2024) |
| Pregnant or breastfeeding | Up to 200 mg a day | EFSA 2015; the FDA advises asking your health care provider |
| Children and adolescents | 3 mg per kg of body weight a day | EFSA 2015 |
| Before sleep | 100 mg close to bedtime may affect sleep in some adults | EFSA 2015 |
Typical caffeine in drinks
- Brewed coffee: 113–247 mg per 12 fl oz (FDA) — the preset uses the middle, 180 mg.
- Espresso: about 80 mg a shot; a cup of tea about 50 mg (EFSA’s examples).
- Black tea 71 mg and green tea 37 mg per 12 fl oz; cola 23–83 mg per 12 fl oz can; energy drinks 54–328 mg per 16 fl oz (FDA). Instant coffee, chai and filter coffee vary widely — use the label or the café’s figure where you can.
- Pair this with the sleep calculator to plan a bedtime, and the water intake calculator for fluids.
Caffeine Calculator FAQ
How much caffeine is too much?
For most healthy adults, up to 400 mg a day spread through the day does not raise safety concerns according to EFSA and the FDA; in pregnancy and breastfeeding EFSA’s figure is 200 mg.
How do I use the caffeine calculator for sleep?
Enter your drinks with their times and your bedtime. The caffeine calculator estimates how much is left when you go to bed and when it drops below 100 mg.
How long does caffeine stay in your body?
Half of it is usually gone in 3–7 hours, but some remains for much longer: after two half-lives a quarter is still there.
How do I work out caffeine by weight?
Divide your daily caffeine in mg by your weight in kg. EFSA’s adult figure is about 5.7 mg/kg a day; for children and teenagers it is 3 mg/kg.
How much caffeine is in a cup of coffee?
It varies a lot: an 8 fl oz brewed coffee has roughly 75–165 mg, an espresso about 80 mg. Use the label or café figure when you have it.
Is this caffeine calculator medical advice?
No. It gives estimates for information. People react to caffeine very differently, so ask your doctor if you have questions about your intake.