Pre-Workout Caffeine Timing Calculator
Time your pre-workout caffeine so it peaks during training — and see how much is still in your system at bedtime given caffeine’s ~5-hour half-life.
How it works
Peak effect ≈ 45–60 min after intake · Remaining = dose × 0.5^(hours ÷ 5) (5-hour half-life)
Caffeine blood levels peak roughly 45–60 minutes after you swallow it, so taking your pre-workout dose about an hour before training lines the peak up with your session. It then clears with a half-life of about five hours, meaning half remains after five hours, a quarter after ten. Because even ~50 mg lingering at bedtime can disturb sleep for sensitive people, this tool also shows how much is left when you plan to sleep.
Worked example
A 200 mg dose taken 8 hours before bed leaves 200 × 0.5^(8 ÷ 5) = 200 × 0.5^1.6 ≈ 66 mg still circulating at bedtime — enough to affect a light sleeper, so an afternoon session might call for a smaller dose or an earlier one.
Frequently asked questions
When exactly should I take pre-workout caffeine?
About 45–60 minutes before you start, so the blood level peaks during the hardest part of your session. Powders and pills act on a similar timeline to coffee.
Will it wreck my sleep?
It can if too much remains at bedtime. With a ~5-hour half-life, a late-day dose can leave meaningful caffeine at night — this tool estimates how much so you can adjust the timing or amount.
Does everyone clear caffeine at the same rate?
No. Genetics, smoking, pregnancy and some medications shift the half-life from roughly 3 to 7+ hours, so treat the 5-hour figure as an average.
Related calculators
Educational estimate, not medical advice. Talk to a doctor, pharmacist or registered dietitian before starting or changing any supplement, especially if you are pregnant, nursing, on medication or managing a health condition.