Caffeine Half-Life: Why a Late Coffee Lingers
Caffeine does not vanish when the cup is empty. The half-life curve explains why an afternoon coffee can still be felt at night.
What is the Caffeine Half-Life Calculator?
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.
How to use it
- Enter the caffeine dose in milligrams.
- Enter how many hours have passed.
- Click Estimate Remaining Caffeine.
Worked example
200 mg after 6 hours with a 5-hour half-life leaves about 87.05 mg, roughly 43.53 percent of the dose.
How long until caffeine is mostly gone?
After about four to five half-lives only a small fraction remains, which for a 5-hour half-life means roughly a day. That is a rule of thumb, not a guarantee.
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.