Caffeine Half-Life Calculator
Estimate a range of caffeine remaining from user-set half-life scenarios without claiming a sleep, safety or medical threshold. Sensitive inputs stay in your browser.
After 8 hours, a one-compartment half-life range of 3–7 hours gives a midpoint estimate of 49.5 mg.
Context matters.
- Caffeine half-life varies with pregnancy, age, smoking, liver function, medications and other factors. Use a clinician-provided range when relevant.
- This decay illustration cannot determine sleep quality, impairment, dosing, treatment or an individual's measured caffeine level.
Sources & scope
The calculation guide and this source trail show what the result means, where the rule came from and when it was last reviewed. This is source-and-calculation QA, not a claim of medical, legal, tax or other professional review; time-sensitive decisions still belong with the linked authority.
A visible path from input to answer.
Estimate a range of caffeine remaining from user-set half-life scenarios without claiming a sleep, safety or medical threshold. The page keeps the calculation scope and its limits beside the result so the output can be checked, copied or revisited.
- Read the record. The calculator uses Caffeine consumed (mg), Intake date, Intake time, Estimate remaining on and Estimate remaining at and 3 additional fields supplied in the form.
- Apply the scope. It applies the Educational one-compartment caffeine-decay range — no sleep, impairment, dosing or measured-level conclusion reference and the explicit date, unit and counting conventions shown in the result.
- Expose the checkpoints. Intermediate rows, warnings and timeline events stay visible; the emphasized row identifies the primary checkpoint when one exists.
After 8 hours, a one-compartment half-life range of 3–7 hours gives a midpoint estimate of 49.5 mg.
- Remaining estimate range23.6–67.9 mg
Calculation purpose: Estimate a range of caffeine remaining from user-set half-life scenarios without claiming a sleep, safety or medical threshold. This is a high-sensitivity reference output; the linked authority or qualified professional controls the final decision.
Calendar inputs use plain year-month-day semantics. Leap days, month ends, date-pair order and unsupported dates are checked before the result is shown.
Rule set 1.1.0 · Last reviewed 2026-08-23 · Next review due 2027-02-23. The source panel below contains the linked evidence.
What to know before using the result.
How long does caffeine last?
Caffeine declines gradually rather than switching off at one time. The calculator shows a remaining-amount range using the lower and upper half-life scenarios entered.
Is five hours the same for everyone?
No. Published references describe substantial variation with pregnancy, age, smoking, liver function, medicines and other factors.
Can this tell me when caffeine will stop affecting sleep?
No. The optional milligram marker is only a display marker and does not determine sleep quality, impairment or a medical threshold.