How to use the caffeine intake calculator
- List each drink in What you drank: a name, the servings, the caffeine per serving in milligrams and the time. The three drinks shown are examples; replace them with your own.
- Add a row for each extra drink, up to ten.
- Enter your bedtime and a half-life in hours. The 5 hours shown is an example, because the speed varies a lot from person to person.
- Read the total consumed, the estimated amount left at bedtime and the table for each drink.
Formula
Caffeine for a drink = servings x milligrams per serving
Left at bedtime = caffeine x 0.5^(hours before bed / half-life)
Total = sum over all drinks
Each drink decays on its own along a smooth curve that halves every half-life. A drink with a clock time later than bedtime is counted as the previous day. The tool does not model how fast caffeine is absorbed.
Coffee, tea and cola
One coffee (95 mg) at 08:00, one tea (45 mg) at 13:00 and one cola (35 mg) at 16:00 add up to 175 mg. With bedtime at 22:30 and a 5 hour half-life, the coffee is 14.5 hours before bed and 12.7 mg of it is left, the tea 9.5 hours before with 12.1 mg left and the cola 6.5 hours before with 14.2 mg left. About 39 mg, or 22.3 percent, remains at bedtime.
With a 6.5 hour half-life and bedtime at 23:00, two 80 mg coffees at 07:00 and one 160 mg cold brew at 14:30 total 320 mg, and about 93.7 mg remains. A 100 mg espresso at 23:00 with bedtime at 01:00 and a 4 hour half-life leaves 70.7 mg after two hours.
What the numbers mean and do not mean
The page adds up what you enter and draws a smooth decay curve. The amounts of caffeine in a drink depend on the brand, the size, the beans and the brewing, so the values shown are only examples. A half-life of 5 hours is also an example, since it can be much shorter or longer for different people and situations. The results are informational. They are not a measurement and do not say what is a healthy or safe amount, which is a question for a doctor or pharmacist.
If you want to see how caffeine and sleep might fit around your day, the Hours Slept Calculator and the Sleep Cycle Calculator plan times to sleep and wake.
Getting the inputs right
Check the label of a packaged drink for its caffeine content, and weigh up a large cup of coffee as more than one serving. Enter each cup as its own row when the times are different, because the time shifts how much is left at bedtime. To set the right amount of fluids across the day, the Water Intake Calculator gives a planning range, and the TDEE Calculator estimates energy use for an active day.
Assumptions and limits
- The milligrams per serving and the half-life are numbers you enter. The values shown are examples, not facts about any drink or person.
- Caffeine decays smoothly with one half-life and nothing else changes it.
- Bedtime is on the same day as the drinks unless a drink is later than bedtime, which counts as the day before.
- This is for information only, is not medical advice and stays in your browser.
Frequently asked questions
How do I work out how much caffeine I have had?
Multiply the number of servings by the milligrams in each and add up the drinks. The page does this for each row and shows the total.
What is a caffeine half-life?
It is the time it takes for half of the caffeine in your body to be cleared. After two half-lives a quarter is left. The number differs between people, so the 5 hours shown is only an example.
How much caffeine is in a cup of coffee?
It varies widely with the beans, the size and the brewing method. Check the label or the shop's information, and enter that number, because the 95 mg shown is just an example.
Does the page tell me how much is too much?
No. It does not set limits and gives no medical advice. Talk with a doctor or pharmacist about what is right for you.