Caffeine Half-Life Calculator
Estimate how much caffeine is still in your system after a coffee, espresso or energy drink. Enter your dose and half-life to see the amount left at any hour and when you fall below a sleep-safe 50 mg.
How to use the caffeine half-life calculator
- Enter your caffeine dose in milligrams, or pick a common drink preset.
- Adjust the half-life slider if yours differs from the 5 hour average.
- Set how many hours have passed to see the caffeine remaining and your sleep-safe time.
Examples
200 mg coffee, 5 hours later
Dose 200 mg, half-life 5 hours, 5 hours elapsed
100 mg remaining (50% of the dose); under 50 mg after about 10 hours
Slow metabolizer, 12 hour half-life
Dose 200 mg, half-life 12 hours, 8 hours elapsed
About 126 mg remaining; it takes roughly 24 hours to drop under 50 mg
Frequently asked questions
What is the half-life of caffeine?
Half-life is the time for half the caffeine to clear your body. For a healthy adult it averages about 5 hours, so a 200 mg coffee leaves about 100 mg after 5 hours and 50 mg after 10 hours.
Does everyone clear caffeine at the same rate?
No. Half-life varies a lot between people. It can be as short as 2 to 3 hours in fast metabolizers and stretch past 9 hours in others. Pregnancy, liver conditions and some medicines can push it beyond 15 hours, while smoking shortens it. Adjust the slider to match your own pace.
How long before bed should I stop drinking coffee?
Aim to be under about 50 mg of caffeine by bedtime, since higher levels can fragment sleep. With a 5 hour half-life a 200 mg coffee crosses that line near 10 hours, so an early-afternoon cutoff is a safe default. Use the sleep-safe readout to time your last cup.
How much caffeine is in common drinks?
Rough averages: brewed coffee about 95 mg per cup, espresso about 63 mg per shot, a typical energy drink about 80 mg, black tea about 47 mg and cola about 34 mg. Actual amounts vary by brand, bean and serving size.
How is the remaining caffeine calculated?
It uses exponential decay: remaining equals dose times 0.5 raised to the power of hours divided by half-life. Each half-life cuts the amount in half, so the level falls quickly at first and then tapers off.
Is my data sent anywhere?
No. The whole calculation runs in your browser. Your dose, half-life and timing never leave your device and nothing is stored or uploaded.
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