Caffeine cutoff calculator

Enter your bedtime and what you drank today. The calculator suggests when to have your last caffeine, using benchmarks from a 2023 research review, and estimates how much is still in your system at bedtime.

Runs in your browser. Nothing you enter is stored or sent anywhere.

How the caffeine calculator works

It gives you two numbers.

A cutoff time. A 2023 systematic review and meta-analysis pooled 24 studies and found that caffeine cut total sleep time by about 45 minutes on average, reduced sleep efficiency by 7%, and added about 9 minutes to the time it took to fall asleep and 12 minutes of time awake after first falling asleep. From those data, the authors suggested having a standard coffee (about 107 mg per 250 mL) at least 8.8 hours before bed, and a larger dose such as a pre-workout supplement (about 217.5 mg) at least 13.2 hours before[1]. The calculator uses whichever of the two benchmarks is closest to your largest drink.

What’s left at bedtime. Caffeine leaves the body gradually. In healthy adults its half-life, the time for the level to fall by half, is usually 3 to 7 hours, and blood levels peak about two hours after a drink[3]. The calculator uses a simple half-life model (5 hours unless you change it) to estimate how much caffeine from each drink remains when you lie down, and shows the range for a fast or slow half-life.

Why caffeine reaches so far into the evening

In a small lab study, 12 healthy adults took 400 mg of caffeine (the FDA puts 400 mg at about two to three 12-ounce cups of coffee[5]) at bedtime, 3 hours before, or 6 hours before. Even the dose taken 6 hours before bed reduced measured total sleep by more than an hour, and the authors suggested avoiding substantial caffeine for at least 6 hours before bed[2]. The later review suggests the window can be longer still for typical drinks[1].

People also differ a lot. One liver enzyme, CYP1A2, handles about 95% of caffeine breakdown, and genes, smoking, hormones and medicines all change how fast it works[4]. Smoking roughly doubles how fast caffeine is cleared, oral contraceptives can roughly double its half-life, and in pregnancy the half-life gets considerably longer[3]. If you are pregnant, the FDA advises asking your health care provider about caffeine[5].

About the drink amounts

The presets are rough. The FDA lists 12 ounces of brewed coffee at about 113 to 247 mg, black tea at about 71 mg, green tea at about 37 mg, soft drinks at about 23 to 83 mg and energy drinks at about 41 to 246 mg, and an 8 ounce decaf at about 2 to 15 mg. The FDA cites 400 mg a day as an amount not generally associated with negative effects for most adults, though sensitivity varies widely[5]. Check the label of your own drink if it lists caffeine.

Using the result

• If your last drink lands after the cutoff, try moving it earlier by an hour a week, or switch the afternoon cup to decaf or green tea.
• If you nap, plan the coffee around it with the nap alarm calculator.
• Pick a realistic bedtime first. The sleep cycle calculator can suggest one from your alarm time.
• Still wired at bedtime? A few minutes of slow, paced breathing or a low, steady sound like brown noise may make the wait more comfortable.

This tool gives general estimates for healthy adults and is not medical advice. If you are often tired despite enough time in bed, snore loudly, or struggle to sleep on most nights, talk to a doctor or a sleep specialist.