Question 1

How long does caffeine stay in your body?

Accepted Answer

Half of it is usually gone after 3 to 6 hours, and the rest keeps halving at the same pace. A 95 mg cup of drip coffee at 2 pm peaks at about 82 mg an hour later, is down to about 50 mg by 7 pm and still leaves about 33 mg at 10 pm with a 5-hour half-life. Add your own drinks above to see your curve, or see how long caffeine lasts hour by hour.

Question 2

What is the half-life of caffeine?

Accepted Answer

For most adults it is between 3 and 6 hours. Smoking speeds up how fast caffeine is cleared and oral contraceptives slow it down, so your own half-life can sit outside that range. The calculator starts at 5 hours; change it to match you. More on caffeine half-life.

Question 3

How much caffeine is too much in a day?

Accepted Answer

For most healthy adults, the U.S. Food and Drug Administration cites 400 mg a day, about two to three 12-ounce cups of coffee, as an amount not generally associated with negative effects. The European Food Safety Authority reaches the same daily figure and adds that single doses up to 200 mg raise no safety concerns for healthy adults.

Question 4

When should I stop drinking coffee before bed?

Accepted Answer

In a study where people took 400 mg of caffeine at bedtime, 3 hours before or 6 hours before, all three disrupted sleep compared with a placebo, and the authors recommend avoiding substantial caffeine for at least 6 hours before bed. Smaller amounts wear off sooner: set your bedtime above and the calculator shows how much will be left and when you drop below your sleep threshold. More on caffeine and sleep.

Question 5

How much caffeine is safe during pregnancy?

Accepted Answer

The European Food Safety Authority concludes that up to 200 mg a day from all sources raises no safety concerns for the unborn child. Talk to your doctor or midwife about what is right for you. More on caffeine during pregnancy.

Question 6

How accurate is this calculator?

Accepted Answer

It uses a standard pharmacokinetic model with the absorption speed of each drink and a half-life you can adjust, the same model the Caffeine Clock app uses. Real levels differ from person to person (smoking and oral contraceptives are two known reasons), so treat the numbers as an estimate rather than a measurement.

Caffeine calculator

My consumption

How the calculator works

Frequently asked questions