Caffeine Half-Life Calculator
Estimate how much caffeine is still in your system hours after a drink.
Quick answer: enter your details below and click Estimate Remaining Caffeine — your result appears instantly, right here in your browser. Nothing you enter is uploaded or stored.
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How to use
- Enter the caffeine dose in milligrams.
- Enter how many hours have passed.
- Click Estimate Remaining Caffeine.
About this tool
Caffeine fades by roughly half every few hours, so a late coffee can still leave a noticeable amount at bedtime. Enter the dose, the hours since you drank it, and the half-life, and the tool applies the decay curve. The result is an estimate — real half-lives vary by person.
Frequently asked questions
What is a typical half-life?
Around 5 hours is a common average, but values from about 3 to 7 hours are normal for many adults.
Does this measure sleepiness?
No, it estimates the amount remaining, not how alert or sleepy you will feel.