A healthy adult night is not one flat state. You cycle through light, deep, and REM sleep about every 90 minutes, and caffeine late in the day cuts into the deep and REM shares first.

Horizontal bar chart of adult sleep architecture: light sleep 50 percent, REM sleep 25 percent, deep sleep 20 percent, awake 5 percent — Typical adult sleep architecture across a full night, by share of total sleep time.

Approximate shares for healthy adults; proportions shift with age, alcohol, and late caffeine.

FAQ

Frequently Asked Questions

Free Tool

Caffeine Cutoff Calculator

Caffeine has a half-life of about 5 hours, so half of your last coffee is still in your blood 5 hours later. Enter your bedtime and your usual dose, and this calculator shows the latest time you can drink caffeine and still be near a sleep-safe 50 mg at lights out.

Bedtime Caffeine dose (mg) How fast do you metabolize caffeine?

Method: residual caffeine follows exponential decay, dose × 0.5^(hours ÷ half-life). The 50 mg sleep threshold and ~5h average half-life come from published caffeine pharmacokinetics; individual half-life ranges from about 2 to 9 hours. Educational tool, not medical advice.

Chart of caffeine half-life: a 200 mg dose decays to 100 mg after about 5 hours and 50 mg after about 10 hours — Caffeine decays exponentially: about half of your dose is still active 5 hours after drinking it.

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