Caffeine Half-Life Calculator

How much caffeine is still in your system, and when it is low enough to sleep.

5 hourshours
Average is about 5 hours. Smokers metabolise faster (~3 h); pregnancy, some medicines and oral contraceptives slow it (7-10 h).
mg
Many people sleep fine below ~50 mg; sensitive people may need less.
95Caffeine consumedmg
1:38 PMBelow 50 mg at4.6 h after drinking
48After 5 h (one half-life)mg remaining
Remaining after 3 hours
63 mg
Remaining after 6 hours
41 mg
Remaining after 12 hours
18 mg
Practically gone (< 10 mg) at
1:14 AM

Caffeine remaining (mg)

02550751001h: mg in body 82.72h: mg in body 723h: mg in body 62.74h: mg in body 54.65h: mg in body 47.56h: mg in body 41.48h: mg in body 31.310h: mg in body 23.812h: mg in body 1816h: mg in body 10.320h: mg in body 5.924h: mg in body 3.41h2h3h4h5h6h8h10h12h16h20h24hmg in body

Estimates use population-average pharmacokinetics. Individual metabolism varies. Not medical advice.

About the Caffeine Half-Life Calculator

Caffeine is cleared from the body exponentially: every half-life, the amount remaining halves. For a healthy adult the half-life is roughly five hours, so a 200 mg large coffee at 9 AM still leaves about 100 mg at 2 PM, 50 mg at 7 PM and 25 mg at midnight. That lingering quarter is enough to shorten deep sleep for many people, which is why sleep researchers suggest a caffeine cut-off eight to ten hours before bed.

This calculator applies the formula remaining = dose × 0.5(hours ÷ half-life) to your drink and timing. It tells you how much is in your system at key points, when the level falls under your chosen sleep threshold, and plots the decay curve. Adjust the half-life slider to reflect your own metabolism: genetics, smoking, pregnancy, liver function and several medications all change how fast caffeine is processed.

How to use the Caffeine Half-Life Calculator

  1. Select your drink (or enter a custom caffeine amount) and the number of servings.
  2. Enter the time you drank it and adjust the half-life slider if you know you metabolise caffeine fast or slowly.
  3. Read how much remains at each point and the time your level drops below the sleep threshold.

Frequently asked questions

How long does caffeine stay in your system?

With a five-hour half-life, about 25% of a dose is still present after 10 hours and around 6% after 20 hours. It takes roughly a day for a normal dose to become negligible.

What time should I stop drinking coffee?

A common rule is no caffeine within 8 to 10 hours of bedtime. If you sleep at 11 PM, make your last coffee around 1 to 3 PM. The calculator gives a personalised time based on your dose and threshold.

How much caffeine is safe per day?

Up to 400 mg per day is considered safe for most healthy adults (about four 8-oz coffees). Pregnant women are typically advised to stay under 200 mg. Sensitivity varies widely.

Why does caffeine affect me more than my friends?

Variants of the CYP1A2 liver enzyme make some people "slow metabolisers" with a half-life of 8 hours or more. Age, body weight, medications and habitual intake also matter.