Caffeine Half-Life Calculator
See how much caffeine is still in your system and when it wears down toward a quarter cup or nearly gone. Default half-life is 5 hours.
How to use this caffeine half-life calculator
Caffeine half-life answers “when will this wear off?” An 8 oz brewed coffee is often ~95 mg; energy drinks and shots vary widely. Average adult half-life is about five hours, so a 3 p.m. coffee can still be a quarter-strength at 10 p.m.
Pregnancy, oral contraceptives, liver disease, and some medicines can double half-life. Smoking can shorten it. This is pharmacokinetics 101, not a medical test. Avoid caffeine within 8–10 hours of bedtime if you sleep poorly — check remaining mg on this page, then pick a bedtime on the Sleep Calculator.
Formula
Worked example
A 95 mg coffee 3 hours ago with a 5-hour half-life leaves about 63 mg. It takes a few more hours to fall near 25 mg (a quarter cup) and longer to reach ~5 mg.
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Frequently asked questions
How long does caffeine last?
Roughly half is gone in 5 hours for a typical adult. A quarter remains after 10 hours. Sensitivity varies.
How much caffeine is in a cup of coffee?
Often 80–100 mg for 8 oz drip. Espresso shots are ~60–75 mg. Check your label.
When will caffeine wear off enough to sleep?
Many people want remaining under ~25–50 mg. This tool shows hours until 25 mg and 5 mg.
Can I change the half-life?
Yes. Use 3 hours if you clear caffeine fast, 7+ if you are sensitive or pregnant (and ask a doctor about caffeine at all).
Is remaining mg the same as feeling jittery?
Not exactly. Tolerance, sleep debt, and anxiety change how the same milligrams feel.
Results are estimates for informational purposes and are not financial, legal, or professional advice. Last reviewed 2026-08-20.