How much caffeine helps you, and how late you can have it, depend heavily on how fast you clear it, and people differ by a factor of five or more. This calculator works out your personal dose range and the time after which a coffee will still be in your system at bedtime.
Last call for a 240 mg dose today: 4:41 PM. After this, residual at bedtime clears the threshold.
Educational estimate, not medical advice. Doses are evidence-based ranges, not prescriptions; test tolerance in training. Never dose caffeine powder without a milligram scale, one teaspoon can be a lethal dose. If you have a heart condition, are pregnant, or take medication, consult a clinician.
The ergogenic range widely supported in the literature sits at roughly three to six milligrams per kilogram of bodyweight taken about an hour before training. Below that the effect is unreliable, and above it side effects rise without further performance benefit for most people.
A common variant in the CYP1A2 gene largely determines how quickly you clear caffeine. Fast metabolisers benefit across the full dose range. Slow metabolisers get the performance benefit at lower doses and gain little from more, while the sleep disruption and jitteriness scale up regardless.
You do not need a genetic test to make use of this. How caffeine actually affects you is a serviceable proxy, and the calculator accepts either. Smoking accelerates clearance substantially, while oral contraceptives and pregnancy slow it considerably.
Caffeine has a half life of roughly five hours on average, but ranging from around two to over fifteen depending on the individual. That means an afternoon coffee can leave a meaningful amount in your bloodstream at midnight. The tool computes your personal last call time, the point after which a given dose will still be above the threshold that disrupts sleep when you go to bed.
Training stimulants are only one piece of the picture — make sure your Calorie & TDEE and protein targets are dialed in too, since sleep quality feeds back into recovery and appetite as much as caffeine timing does.
Around three to six milligrams per kilogram of bodyweight, taken roughly forty five to sixty minutes beforehand, is the range best supported for performance. Slow metabolisers often do better nearer the bottom of that range.
The average half life is about five hours, so half remains after five hours and a quarter after ten. Individual half lives range from roughly two to fifteen hours, which is why the same afternoon coffee ruins one person's sleep and not another's.
It depends on your dose and your clearance rate. For an average metaboliser, eight to ten hours before bed is a reasonable rule for a substantial dose. Slow metabolisers may need considerably longer.
Health authorities generally consider up to 400 mg daily safe for healthy adults, with no more than about 200 mg in a single dose. Pregnancy guidance is lower, at around 200 mg per day.
Tolerance develops to some effects, particularly alertness, more than to others. Habitual users still see performance benefits, though cycling intake periodically can restore sensitivity.
