What does caffeine half-life mean?
Half-life is the time required for an amount to decrease by half. Caffeine clearance varies with genetics, pregnancy, smoking, medications, liver function, and other factors; its effects also depend on individual sensitivity.
An exponential-decay estimate
The model starts with the entered dose and assumes immediate absorption and a constant half-life from 2–10 hours, defaulting to five. It shows the estimated remaining amount and time from the dose to 25 mg, an arbitrary comparison threshold rather than a safe or sleep-compatible level.
How to use this calculator
- 1Enter the caffeine dose in milligrams, using a product label when available.
- 2Enter hours since that dose and choose an assumed half-life.
- 3Calculate and compare the remaining amount across different assumptions.
Understanding your result
An estimated amount remaining is not a measure of alertness, impairment, sleep quality, or safety. This single-dose model does not automatically include earlier coffees, tea, energy drinks, supplements, or medicines containing caffeine.
Assumptions & limitations
- Actual absorption takes time, and individual clearance may fall outside the selected range.
- The 25 mg display threshold is arbitrary; no displayed amount establishes when caffeine is safe for you or when sleep will be unaffected.
Frequently asked questions
How much caffeine is in a cup of coffee?+
It varies widely with serving size, beans, and preparation. Use the product's stated caffeine amount when possible rather than assuming every cup is identical.
Does caffeine reach zero after two half-lives?+
No. After two half-lives the model leaves one-quarter of the original dose. Exponential decay approaches zero rather than reaching it at a fixed time.
Is 400 mg a recommended daily target?+
No. FDA cites 400 mg per day as an amount not generally associated with negative effects for most adults, but individual sensitivity and health circumstances can require less.
Can this tell me when it is okay to sleep?+
No. Sleep effects depend on sensitivity, timing, habitual use, and other factors. The amount remaining and 25 mg threshold are not sleep predictions.
