Caffeine Intake & Half-Life Calculator
Today’s caffeine against EFSA and FDA guidance, and how much is left at bedtime.
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Today
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Caffeine in your body
| Time | Event | In your body |
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For general information only, not medical advice. Consult a qualified health professional for advice about your situation.
About the Caffeine Intake & Half-Life Calculator
Add what you drink today — brewed or instant coffee, espresso, latte, tea, cola, energy drinks, chocolate or any amount in milligrams — with the time, and see your total caffeine against official guidance: 400 mg a day for most healthy adults (EFSA and the US FDA), 200 mg a day in pregnancy and while breastfeeding (EFSA), and 3 mg per kg of body weight a day for children and teenagers (EFSA).
A decay curve shows how much caffeine is still in your body through the day, using an adjustable half-life — EFSA gives about 4 hours on average for healthy adults, with a range of 2 to 8 hours. Enter your bedtime and the most caffeine you want left when you go to sleep, and the calculator tells you when you will be below it and the latest time for one more drink. Caffeine contents come from USDA FoodData Central; everything is worked out in your browser and today’s list stays on your device.
How to use it
- Pick a drink and the number of portions (for example 1 cup, or 0.5 for half a can), enter the time you had it and press Add. Use Custom amount for a café drink or a can whose label gives the caffeine in mg.
- Choose who the guidance is for — adult, pregnant or breastfeeding, or child or teenager (with body weight).
- Set your bedtime and the most caffeine you want left at bedtime (50 mg by default). Change the half-life if yours is likely to be shorter or longer.
- Read today’s total, the amount left at bedtime, when it falls below your level and the latest time for one more drink of the kind you pick.
- Copy the summary or download the day as CSV. The list is kept in this browser until tomorrow.
Examples
190 mg today (within 400 mg) · about 27 mg left at 23:00 · peak 128 mg at 14:00
Have it by 19:18 with a 4-hour half-life (4 h × log₂(94.8 ÷ 50) = 3.7 hours before bed)
47 + 47 + 33 = 128 mg — within EFSA’s 200 mg a day for pregnancy
67 mg — above 3 mg/kg (60 mg) for a child of 20 kg
How much caffeine is in drinks
Values from USDA FoodData Central (caffeine per 100 g × the gram weight of the portion):
- Brewed coffee: 95 mg per 8 fl oz cup (237 g); espresso: 63 mg per 1 fl oz shot; instant coffee: 47 mg per 6 fl oz, or 31 mg per teaspoon of powder; latte or cappuccino: 86 mg per 8 fl oz.
- Black tea: 47 mg per 8 fl oz cup; green tea: 29 mg per cup; oolong: 38 mg.
- Cola: 33 mg per 12 fl oz can; diet cola: 43 mg; energy drinks: 75 mg per 8.4 fl oz can (Red Bull) and 164 mg per 16 fl oz can (Monster).
- Dark chocolate (70–85%): 23 mg per ounce; milk chocolate: 9 mg per 44 g bar.
These are averages. The FDA notes that a 12 fl oz serving of brewed coffee can have anywhere from 113 to 247 mg, sodas 23 to 83 mg and energy drinks 41 to 246 mg, and that decaffeinated coffee still has about 2 to 15 mg per 8 fl oz. Café sizes, brewing strength and brands vary, so use the label or the café’s figure when you have it.
How the decay curve is worked out
Taken by mouth, caffeine is absorbed rapidly and completely, and its effects may begin 15 to 30 minutes later (EFSA). The calculator treats each drink as absorbed at once and removed at a constant fraction per hour: amount left = dose × 0.5^(hours since the drink ÷ half-life), summed over every drink. With a 4-hour half-life, 100 mg at 08:00 leaves 50 mg at 12:00 and 25 mg at 16:00; after five half-lives about 3% is left.
The time to fall below a level after the last drink is half-life × log₂(amount ÷ level). The half-life varies widely between people — EFSA lists age, body weight, pregnancy, medicines and liver health as factors — so treat the times as estimates and adjust the half-life if you know you process caffeine more slowly.
The guidance
- Healthy adults: EFSA concluded that intakes up to 400 mg a day spread through the day, and single doses up to 200 mg (about 3 mg/kg), raise no safety concerns; the FDA also cites 400 mg a day for most healthy adults — about two to three 12 fl oz cups of coffee.
- Pregnancy and breastfeeding: EFSA — up to 200 mg a day from all sources does not raise safety concerns for the foetus. ACOG — moderate intake under 200 mg a day does not appear to be a major factor in miscarriage or preterm birth. The FDA suggests talking to your clinician about limiting caffeine if you are pregnant, trying to become pregnant or breastfeeding.
- Children and teenagers: EFSA proposes 3 mg per kg of body weight a day. The FDA page notes that the American Academy of Pediatrics advises against energy drinks for children and adolescents, and US dietary guidelines say children under 2 should avoid caffeinated drinks.
- Sleep: EFSA found that single doses of 100 mg may affect sleep duration and patterns in some adults, particularly close to bedtime.
- Too much: the FDA estimates that toxic effects such as seizures can occur with rapid consumption of around 1,200 mg.
Sources
- EFSA NDA Panel, Scientific Opinion on the safety of caffeine, EFSA Journal 13(5):4102, and EFSA explains risk assessment: Caffeine
- US FDA, Spilling the Beans: How Much Caffeine Is Too Much?
- ACOG Committee Opinion No. 462: Moderate caffeine consumption during pregnancy. Obstet Gynecol 116:467-8
- USDA, FoodData Central (CC0): SR Legacy and FNDDS 2021–2023 — FDC 171890, 171891, 2710386, 174130, 171893, 171889, 173227, 171917, 2710492, 174144, 174871, 174852, 175099, 173210, 2710747, 170273, 167587, 169593
Limitations
- The half-life model is a simplification: absorption takes time, and your own half-life may be much shorter or longer than the one you choose.
- Caffeine contents are averages; brands, brewing and café sizes differ. Indian milk tea (chai) is not in the USDA data: its caffeine depends on how much tea is used, so enter it as black tea or as a custom amount.
- All drink times are on one day, from midnight; a bedtime earlier than your last drink counts as the next morning.
- Caffeine in medicines and supplements is not listed: add it as a custom amount from the pack.
- Not for people with heart conditions, anxiety disorders or other health problems that caffeine can affect — ask your doctor.
Privacy
Everything happens in your browser. What you enter or open here is not uploaded or stored by MySmartCoPilot.
Frequently asked questions
How much caffeine is in a cup of coffee?
USDA FoodData Central lists 95 mg for an 8 fl oz (237 ml) cup of brewed coffee, 63 mg for a single espresso and 47 mg for 6 fl oz of instant coffee. Strength varies: the FDA gives 113–247 mg for a 12 fl oz brewed coffee.
How much caffeine is too much in a day?
For most healthy adults, EFSA and the FDA say up to 400 mg a day, spread through the day, is not associated with harm — about four 8 fl oz cups of brewed coffee. EFSA also says single doses up to 200 mg are of no concern.
How much caffeine is safe in pregnancy?
EFSA says up to 200 mg a day from all sources does not raise safety concerns for the foetus, and ACOG says under 200 mg a day does not appear to be a major factor in miscarriage or preterm birth. That is about two 8 fl oz cups of brewed coffee or four cups of black tea.
What is the half-life of caffeine?
EFSA gives an average of about 4 hours in healthy adults, with a range of 2 to 8 hours. It varies with age, body weight, pregnancy, medicines and liver health. After one half-life half the caffeine is left; after five, about 3%.
When should I stop drinking coffee before bed?
It depends on how much is still in your body. With a 4-hour half-life, a 95 mg coffee falls to 50 mg after about 3.7 hours, so for a 23:00 bedtime you would have it by about 19:18. EFSA notes that 100 mg close to bedtime may affect sleep in some adults.
How much caffeine can children and teenagers have?
EFSA proposes 3 mg per kg of body weight a day — 120 mg for a 40 kg child. The American Academy of Pediatrics advises against energy drinks for children and adolescents.