Caffeine Half-Life Calculator

Find out how much caffeine will still be in your system at bedtime — and when it will fully clear.

General information only. Not medical advice. Caffeine metabolism varies by individual.

What did you drink?

How many?

Total caffeine

95mg

Time you drank it

Your bedtime

Frequently Asked Questions

What is the half-life of caffeine?

Caffeine has a half-life of approximately 5 to 6 hours in most healthy adults. This means that 5 hours after drinking a coffee, roughly half the caffeine is still in your system.

Why does caffeine affect my sleep even hours later?

Because the half-life is 5-6 hours, a coffee at 3pm still has 25% of its caffeine active at 1am. This is enough to reduce deep sleep quality even if you fall asleep normally.

Does the half-life vary by person?

Yes significantly. Pregnancy, some medications, liver conditions, and genetics all affect caffeine metabolism. Smokers metabolise it faster, pregnant women much slower.

Is this medical advice?

No. This is general informational content only. Consult a healthcare provider for advice specific to your health situation.

How much caffeine is in a typical coffee?

A standard espresso has around 63mg, a drip coffee around 95mg, and energy drinks typically 80-150mg. The calculator lets you select your drink type.

Caffeine Half-Life: What Happens After Your Morning Coffee

Caffeine is absorbed rapidly after oral consumption — reaching peak blood concentration within 30–60 minutes. Its effects on alertness, heart rate, and focus stem primarily from blocking adenosine receptors. Adenosine is the molecule that accumulates during waking hours to create sleep pressure; when caffeine blocks its receptors, you feel less drowsy without reducing actual adenosine levels.

The 5–6 hour half-life

In healthy adults, caffeine has a plasma half-life of approximately 5–6 hours. This means that 5–6 hours after your last caffeine intake, roughly half the dose is still active in your bloodstream. After 10–12 hours, approximately 25% remains. This is why a 3pm coffee can still be affecting sleep quality at midnight — particularly the deep slow-wave sleep stages that dominate early in the night.

The cutoff time for afternoon caffeine that sleep researchers most commonly recommend is 2–3pm for people with a standard 10–11pm bedtime. The goal is to have caffeine levels below a meaningful threshold by sleep time, not zero — a rough guideline is under 100mg remaining.

Individual variation in metabolism

Caffeine metabolism varies significantly between individuals due to genetic differences in the CYP1A2 enzyme. Smokers metabolise caffeine up to 50% faster. Pregnant women metabolise it up to four times slower — reaching 15+ hour half-lives in the third trimester. Certain medications (oral contraceptives, some antibiotics, fluvoxamine) inhibit caffeine metabolism and significantly extend its half-life. Liver disease also reduces clearance rate.

Tolerance and dependence

Regular caffeine consumers develop tolerance to its alertness-enhancing effects within 1–4 days of consistent use at the same dose. The physical dependence effects (withdrawal headaches, fatigue) are real but mild and typically resolve within 48–72 hours of cessation. Withdrawal is not medically dangerous for healthy adults.