Coffee Kick Calculator

An afternoon coffee still has half its caffeine in you five hours later.

Still circulating at bedtime62.7 mgafter 8 hours, at a 5-hour half-life

Caffeine taken190 mg2 × Filter coffee

As a fraction of the dose33%

Equivalent to0.66 fresh filter coffeewhich is the way to think about it

Against the 400 mg daily guidance47.5%

Time to fall below 50 mg9.6 hours

Five hours is an average and the spread is enormous — from two hours in fast metabolisers to eight or more in slow ones, largely down to one liver enzyme. Pregnancy roughly doubles it. People who say coffee does not affect their sleep and people who cannot touch it after lunch are often both right.

The formula

remaining = dose * 0.5 ^ (hours / half-life)

Five hours, halved

Caffeine has a half-life of about five hours in a typical adult, so a 95 mg filter coffee at four in the afternoon still has nearly 50 mg circulating at nine and 25 at two in the morning. That is most of a fresh cup, and it is why an afternoon coffee costs sleep even when it does not feel like it.

The half-life varies enormously

Five hours is the average and the spread is wide: from two hours in fast metabolisers to eight or more in slow ones, largely down to a single liver enzyme. Pregnancy roughly doubles it, and oral contraceptives extend it substantially. People who insist coffee does not affect their sleep and people who cannot touch it after lunch are often both telling the truth.

400 mg is the usual daily guidance

Health agencies generally put the limit for healthy adults at 400 mg a day — about four filter coffees — and 200 in pregnancy. The acute toxic dose is far higher, but caffeine powder sold as a supplement has caused deaths precisely because a teaspoon is already several times a safe dose.

Recipes are starting points

Ovens run hot or cold by 20 degrees, flour absorbs water differently by season and brand, and the same joint of meat cooks at a different rate depending on its shape rather than its weight. Everything here is a planning figure that gets you close enough to start, and the thermometer, the scales and your own notes from last time are what finish the job.