Daily caffeine is about two questions: how much, and when
Health Canada sets the daily caffeine limit for healthy adults at 400 mg, which is about four 8 oz cups of brewed coffee at roughly 95 mg each. Pregnant and breastfeeding women, and those planning a pregnancy, are advised to stay at 300 mg, and children and teens under 18 at 2.5 mg per kilogram of body weight. Staying under the number is only half of it. Caffeine from a late-afternoon drink is still in your body at bedtime: with an average half-life of about 5 hours, 200 mg at 3 PM leaves roughly 66 mg at 11 PM.
This calculator takes each drink and the time you had it, adds them up against the limit that applies to you, and draws a curve of the caffeine left in your body through the day, with the amount now and at bedtime. An older version of this tool scaled the limit with a "sensitivity factor" and used a 300 mg figure for older adults. Neither had a published source, so both were dropped.
How to use the calculator
- Choose who it is for: adult, pregnant, breastfeeding or under 18. For under 18, enter a body weight, because the limit is set per kilogram.
- Set bedtime and half-life: enter the time you usually go to sleep. Leave the half-life at 5 hours, or compare 2.5 hours (smokers) and 15 hours (late pregnancy).
- Add your drinks: pick the time, then tap a drink button or type the milligrams from the label.
- Read the result: the limit bar, the amount left, the estimates for now and for bedtime, and the curve all update at once. Your log is kept in this browser only if you switch saving on.
Health Canada daily caffeine limits
| Group | Daily limit | In practice |
|---|---|---|
| Adults (18 and over) | 400 mg | About four 8 oz cups of brewed coffee |
| Planning pregnancy, pregnant or breastfeeding | 300 mg | About three 8 oz cups of brewed coffee |
| Under 18 | 2.5 mg per kg of body weight | 30 kg: 75 mg; 40 kg: 100 mg; 50 kg: 125 mg |
The calculator uses the 300 mg figure for both pregnancy and breastfeeding, as Health Canada does, so the breastfeeding option needs no separate note. These are limits for the whole day, not a target.
How much caffeine is in common drinks
The buttons use USDA FoodData Central (SR Legacy) values per 100 g, scaled to a typical serving, with 100 g treated as 100 ml. Real drinks vary with the bean or leaf, the brewing and the cup size, so use the number on the label whenever there is one.
| Drink | Per 100 g | Serving | Caffeine per serving |
|---|---|---|---|
| Brewed coffee | 40 mg | 8 fl oz | 95 mg |
| Espresso | 212 mg | 1 shot (30 ml) | 64 mg |
| Black tea, brewed | 20 mg | 8 fl oz | 47 mg |
| Green tea, brewed | 12 mg | 8 fl oz | 28 mg |
| Cola | 9 mg | 12 fl oz | 32 mg |
Espresso has far more caffeine per ounce than brewed coffee, but a shot is small, so a single cup of brewed coffee usually has more in total.
Half-life and bedtime
The half-life is the time it takes for the caffeine in your body to fall by half. NCBI StatPearls gives an average of about 5 hours for adults, up to 50% shorter in smokers and up to 15 hours in late pregnancy. This is how much of 200 mg taken at 3 PM remains (mg):
| Time | Half-life 2.5 h | 5 h | 15 h |
|---|---|---|---|
| 5 PM | 115 | 152 | 182 |
| 8 PM | 50 | 100 | 159 |
| 11 PM | 22 | 66 | 138 |
| 2 AM | 9 | 44 | 120 |
The example log (8:00 AM brewed coffee 95 mg, 12:30 PM espresso 64 mg, 3:30 PM black tea 47 mg) adds up to 206 mg, about 52% of the adult limit. With a 5-hour half-life, around 43 mg of that is still in your body at 11 PM.
Other countries set slightly different numbers
- Health Canada: adults 400 mg; pregnant, breastfeeding or planning a pregnancy 300 mg; under 18, 2.5 mg per kg.
- EFSA (European Food Safety Authority, 2015): adults 400 mg a day and single doses up to 200 mg (about 3 mg per kg for a 70 kg adult); pregnant 200 mg; breastfeeding 200 mg; children and adolescents 3 mg per kg.
- South Korea (MFDS): adults 400 mg, pregnant women 300 mg, children and teens 2.5 mg per kg.
All three agree on 400 mg for adults. They differ on pregnancy, breastfeeding and children.
Common mistakes
- Counting cups instead of milligrams: a 12 oz cola has about a third of the caffeine of an 8 oz cup of brewed coffee. Add up the milligrams.
- Thinking only coffee counts: black tea, green tea and cola all contain caffeine, and so do many other products.
- Assuming a daily total under the limit means no effect at night: caffeine from a late drink is still there at bedtime, however low the day's total.
- Using the adult limit for a teenager: at 2.5 mg per kg, a 40 kg child has a limit of 100 mg a day.
Limits of this calculator
- The amount in your body is a simple estimate: each drink is treated as fully absorbed at the moment you drink it and then halves every half-life. In reality, absorption takes time, and body, medication, smoking and pregnancy change the result.
- The drink buttons are USDA averages, so a particular product can contain more or less.
- If you have a heart condition or an anxiety disorder, or take medication, talk to your doctor about how much caffeine is right for you.
- Your log is kept in this browser only if you turn saving on, and it is never sent to a server.
Data checked The sources below were last checked on 2026-10-10.
Sources
- 01Health Canada: Caffeine in foodsAdults 400 mg, pregnancy and breastfeeding 300 mg, under 18 2.5 mg/kg
- 02EFSA: Scientific Opinion on the safety of caffeine (2015)Adults 400 mg, single dose 200 mg, pregnancy and breastfeeding 200 mg, children 3 mg/kg
- 03NCBI StatPearls: CaffeineAverage adult half-life about 5 hours, up to 50% shorter in smokers, up to 15 hours in late pregnancy
- 04USDA FoodData Central (SR Legacy)Caffeine per 100 g: brewed coffee 40, espresso 212, black tea 20, green tea 12, cola 9
- 05Korea MFDS: maximum daily caffeine intakeAdults 400 mg, pregnant women 300 mg, children and teens 2.5 mg/kg
Frequently asked questions
How much caffeine is safe per day?
Health Canada gives 400 mg a day for adults 18 and over, 300 mg a day for women planning a pregnancy, pregnant or breastfeeding, and 2.5 mg per kg of body weight a day for under 18. A 40 kg teen would have a limit of 100 mg.
How much caffeine is in a cup of coffee?
Using USDA FoodData Central averages, 8 fl oz of brewed coffee has about 95 mg and one espresso shot about 64 mg. Black tea (8 fl oz) is about 47 mg, green tea (8 fl oz) about 28 mg and a 12 fl oz cola about 32 mg. Use the label when there is one.
How much caffeine is left at bedtime?
With an average adult half-life of about 5 hours, 200 mg drunk at 3 PM leaves about 100 mg at 8 PM, about 66 mg at 11 PM and about 44 mg at 2 AM. The half-life varies from person to person.
Is caffeine half-life the same for everyone?
No. NCBI StatPearls gives about 5 hours for the average adult, up to 50% shorter in smokers and up to 15 hours in late pregnancy. You can switch between 2.5, 5 and 15 hours in the calculator to compare.
How much caffeine can I have when pregnant or breastfeeding?
Health Canada advises 300 mg a day for women who are planning a pregnancy, pregnant or breastfeeding. Other bodies set it differently, and EFSA uses 200 mg. Ask your doctor what is right for you.
Do the same limits apply to teenagers?
Not the adult figure. Health Canada sets 2.5 mg per kg of body weight a day for anyone under 18, so a 50 kg teen has a limit of 125 mg. Enter the weight and the calculator works it out.
How accurate is the caffeine curve?
It is a simple estimate. It assumes each drink is absorbed at the moment you drink it and then halves every half-life. In reality absorption takes time and your body, medication and smoking change the result, so treat it as a guide.
Where is my log stored?
By default nothing is saved. If you switch saving on, today's log is kept in this browser only and starts fresh after midnight. Nothing is sent to a server.