Caffeine Half-Life Calculator
Track caffeine clearance and the amount remaining at bedtime.
About Caffeine Half-Life Calculator
Caffeine clears exponentially, so a 200 mg afternoon dose still leaves around 50 mg at bedtime with a five hour half-life. Individual half-life varies several-fold, largely through liver enzyme genetics. Sleep can be measurably disrupted even when someone falls asleep normally, which is why the remaining amount matters more than perceived alertness.
Formula
Caffeine Half-Life
Remaining = dose × (1/2)^(hours ÷ half-life)
- half-life
- Typically 4 to 6 hours but ranges from 2 to 12 between individuals
- clearance
- Slowed by pregnancy, oral contraceptives and liver conditions
Worked example
With the default values below, Caffeine Half-Life Calculator returns Caffeine Remaining Now of 114.87. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Caffeine consumedminimum 0 mg
- 200 mg
- Hours since consumptionminimum 0 h
- 4 h
- Personal half-lifeaccepts 1–12 h
- 5 h
- Hours until bedtimeminimum 0 h
- 6 h
- Body weightaccepts 30–200 kg
- 75 kg
Results
- Caffeine Remaining Now
- 114.87 mg
- Caffeine Remaining at Bedtime
- 50.00 mg
- Half-Lives Elapsed
- 0.800
- Dose per Kilogram
- 2.667 mg/kg
- Sleep Impact Note
- Moderate caffeine remaining — some effect on sleep quality is likely
Step by step
- 1Values used
- 2Caffeine Half-Life
- 3Caffeine Remaining Now= 114.87 mg
- 4Caffeine Remaining at Bedtime= 50.00 mg
- 5Half-Lives Elapsed= 0.800
- 6Dose per Kilogram= 2.667 mg/kg
- 7Sleep Impact Note= Moderate caffeine remaining — some effect on sleep quality is likely
Assumptions and limits
- The result is derived only from the 5 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
- These figures are population-average estimates for training and recreational planning only and are not medical advice. Individual responses vary widely. Consult a qualified health professional before starting or significantly changing an exercise, supplement or nutrition programme, particularly if you have any medical condition.
- This is an estimate for general information and not professional medical advice. See the full disclaimer for the limits that apply to this kind of calculator.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
These figures are population-average estimates for training and recreational planning only and are not medical advice. Individual responses vary widely. Consult a qualified health professional before starting or significantly changing an exercise, supplement or nutrition programme, particularly if you have any medical condition.
Frequently Asked Questions
How is Caffeine Half-Life calculated?
Remaining = dose × (1/2)^(hours ÷ half-life) Caffeine clears exponentially, so a 200 mg afternoon dose still leaves around 50 mg at bedtime with a five hour half-life. Individual half-life varies several-fold, largely through liver enzyme genetics.
Why does Caffeine Half-Life matter?
Sleep can be measurably disrupted even when someone falls asleep normally, which is why the remaining amount matters more than perceived alertness.
What values do I need to enter?
This calculator takes 5 inputs: Caffeine consumed, Hours since consumption, Personal half-life, Hours until bedtime, Body weight. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.