Caffeine Half-Life Calculator
Estimate how much caffeine is left in your body after a set number of hours, using exponential decay and an adjustable half-life.
Calculator by Toolsloft ↗- Caffeine remaining
- 100 mg
- Percent remaining
- 50%
Caffeine has a half-life of roughly five hours, which is why an afternoon coffee can still be working at bedtime. Enter your dose and how long ago you had it to see how much is still circulating, and adjust the half-life if yours runs faster or slower.
How this is calculated
Caffeine follows first-order elimination, so the amount remaining equals the dose multiplied by one half raised to the power of hours elapsed divided by the half-life. The default half-life is five hours, a common average for healthy adults, though pregnancy, smoking, and some medications shift it. The percentage remaining is the remaining amount over the original dose.
How to use
- Enter the caffeine dose in milligrams (a large coffee is roughly 150 to 200 mg).
- Enter how many hours have passed since you consumed it.
- Adjust the half-life if needed, then read how much caffeine remains.
Examples
- 200 mg, 5 hours, 5-hour half-life:
100 mg remaining (50%) - 400 mg, 10 hours, 6-hour half-life:
125.99 mg remaining (31.5%)
FAQ
- What is the half-life of caffeine?
- About five hours on average, meaning half the dose is cleared every five hours. It can range from about three to seven hours depending on genetics, pregnancy, smoking, and liver function.
- How much caffeine is safe before bed?
- Many people notice disrupted sleep with more than about 50 mg in their system at bedtime. Because clearance is slow, cutting off caffeine six to eight hours before bed helps.