Caffeine Calculator
Caffeine at 3–6 mg per kg improves strength, endurance and perceived effort. Its half-life is about five and a half hours, which is why an afternoon dose is still substantially present at midnight.
Your results
General information, not medical advice. If you have a medical condition, are taking medication, or are pregnant, speak to a doctor rather than acting on a number from a web page. Up to 400 mg a day is considered safe for most healthy adults, and lower in pregnancy. Caffeine metabolism varies genetically — some people clear it in half the time others do.
The dose that works
The tested performance range is 3–6 mg per kg of body weight, taken 45–60 minutes before training. Above 6 mg/kg there is no additional performance benefit and side effects rise sharply.
Effects on endurance and repeated efforts are larger than on maximal strength, and the biggest single effect is on perceived effort — the session feels easier at the same load, which often means you complete more of the plan.
Cheapest effective version: a strong coffee or a 200 mg tablet. Almost every pre-workout is caffeine plus ingredients that are either redundant or under-dosed.
Why the sleep arithmetic matters more than the dose
Caffeine's half-life is roughly 5–6 hours, so a 300 mg dose at 6pm leaves around 150 mg in your system at midnight — comfortably enough to reduce sleep quality even if you fall asleep fine.
And this is a losing trade. Sleep restriction reduces exercise performance by around 7.6% on average, with a single restricted night costing 3–5% of maximal strength. Caffeine's benefit is smaller than that. Using caffeine late to train harder borrows against the next few days.
Practical rule: cut it off eight hours before bed. For an 11pm bedtime that means nothing after 3pm.
Common questions
How much caffeine should I take before training?
3–6 mg per kg of body weight, 45–60 minutes before. Start at the lower end.
How long does caffeine stay in your system?
Half-life is about 5–6 hours, so roughly a quarter of the dose remains after 11 hours.
Is coffee as good as pre-workout?
For the caffeine, yes. A double espresso plus daily creatine covers most of the value of a pre-workout.
Should I cycle off caffeine?
Not necessary. Tolerance to the performance effect is partial, and one to two weeks at a low dose restores most sensitivity if you want it back.
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Track the numbers, not just calculate them
MyFitsy stores your weight, measurements and every session, so the figures above become a trend instead of a one-off.
