Caffeine Calculator
See how much caffeine from your coffee, tea or energy drink is still in your body at bedtime, hour by hour, and how today's total compares with the 400 mg guideline.
The pack usually gives it. A mug of brewed coffee often has around 100 mg, a cup of tea or a can of cola far less.
The time it takes the body to clear half of it. About 5 hours is typical, but it ranges from about 1.5 to 9.5 hours between people.
Still in your body at bedtime
66 mg
- Share of the dose left
- 33%
- Down to 50 mg by
- 1:00 am the next day
- Today's total against 400 mg
- 300 of 400 mg
About 66 mg of the 200 mg will still be in your body at 11:00 pm, roughly half a cup's worth.
How it's worked out
- Hours until bed
3:00 pm to 11:00 pm8 hours - Half-lives passed
8 ÷ 51.6 - Left at bedtime
200 × ½^1.666 mg - Time to fall to 50 mg
5 × log₂(200 ÷ 50)10 h
Caffeine left, hour by hour
| Time | In your body |
|---|---|
| 3:00 pm | 200 mg |
| 4:00 pm | 174 mg |
| 5:00 pm | 152 mg |
| 6:00 pm | 132 mg |
| 7:00 pm | 115 mg |
| 8:00 pm | 100 mg |
| 9:00 pm | 87 mg |
| 10:00 pm | 76 mg |
| 11:00 pm | 66 mg |
| 12:00 am | 57 mg |
| 1:00 am | 50 mg |
- Up to 400 mg a day is generally not linked with harm in healthy adults. In pregnancy, the advice is no more than 200 mg a day.
- Children, people with heart conditions and anyone on medicines that interact with caffeine should check with a doctor.
How it is worked out
Caffeine halves every half-life, so the amount left is the dose × ½ raised to (hours passed ÷ half-life). The time to fall to 50 mg is half-life × log₂(dose ÷ 50).
Finding the caffeine in a drink
Check the label: energy drinks and many soft drinks list it. Brewed coffee varies most with the beans, the strength and the size of the cup; tea usually has less than coffee.
Questions people ask
How much caffeine is left at 11 pm from 200 mg at 3 pm?
About 66 mg, with a typical half-life of 5 hours. It falls to 50 mg at around 1 am.
What is caffeine's half-life?
The time it takes your body to clear half of it. About 5 hours is typical for healthy adults, but it ranges widely, from about 1.5 to 9.5 hours between people.
How much caffeine a day is safe?
Up to 400 mg a day is generally not linked with harm in healthy adults. In pregnancy, the NHS advises no more than 200 mg a day.
Does caffeine affect sleep even if I fall asleep fine?
It can. Caffeine still in your body can make sleep lighter and shorter, even when you don't notice it.
About this calculator
Formula and rules last checked 10 November 2026Written and tested by the CalculatorDex teamReport a problem
Sources: FDA: Spilling the Beans, how much caffeine is too much? · NHS: Foods to avoid in pregnancy · Clinical Pharmacology in Drug Development (2018): caffeine half-life in healthy adults