Question 1

How long does caffeine stay in your system?

Accepted Answer

Caffeine has an average half-life of 5–6 hours in healthy adults. That means 100 mg consumed at noon still has roughly 25 mg circulating at midnight. Half-life varies widely with genetics, smoking status, pregnancy, and certain medications.

Question 2

What is the half-life of caffeine?

Accepted Answer

For most adults, the half-life is around 5 hours. Slow metabolizers (CYP1A2 *1F variant) can have half-lives of 8 hours or more. Pregnancy can extend the half-life beyond 10 hours.

Question 3

When should I stop drinking coffee for sleep?

Accepted Answer

A common recommendation is to cut caffeine 8 hours before bed. The calculator above shows your personal cutoff based on dose, half-life, and target bedtime caffeine level.

Question 4

How much caffeine is safe per day?

Accepted Answer

The FDA cites up to 400 mg/day as not associated with negative effects in healthy adults. Pregnant individuals are typically advised to stay under 200 mg/day.

Question 5

Does caffeine sensitivity vary?

Accepted Answer

Yes — substantially. Genetics (CYP1A2), age, body weight, and tolerance all shift sensitivity. Tracking your own sleep, HRV, and resting heart rate response is more reliable than population averages.

Caffeine Half-Life Calculator

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