Caffeine Half-Life Calculator
See how much caffeine is still in your system after a given time. Enter your caffeine dose, the hours that have passed, and caffeine's half-life to find the amount remaining and how long until it drops to a sleep-friendly 50 mg.
- Uses simple first-order decay; individual metabolism varies.
Formula
Remaining = dose × 0.5^(hours / half-life)
- Caffeine clears from the body by first-order (exponential) decay.
- Remaining = dose × 0.5^(hours ÷ half-life).
- After one half-life half the caffeine is left; after two, a quarter; and so on.
- The average adult half-life is about 5 hours, but it ranges from 2 to 12 depending on genetics, pregnancy, and medications.
- Reaching roughly 50 mg — about half a cup of coffee — is a common threshold for sleep-friendly levels.
200 mg, 5 hours later, 5-hour half-life
Inputs
- Caffeine Dose: 200 mg
- Time Elapsed: 5 h
- Caffeine Half-Life: 5 h
After one half-life (5 hours) half the dose is gone, leaving about 100 mg — 50% of the original 200 mg.
Frequently asked questions
What is caffeine's half-life?
It's the time for your body to clear half the caffeine present — around 5 hours on average, but it varies widely between people.
Why does caffeine affect my sleep?
Because of its long half-life, a late-afternoon coffee can still leave meaningful caffeine in your system at bedtime.
What slows caffeine metabolism?
Pregnancy, liver conditions, and some medications (like certain contraceptives) lengthen the half-life, so caffeine lingers longer.
How long before bed should I stop caffeine?
A common guideline is to avoid caffeine for at least 6–8 hours before sleep, but sensitive people may need longer.
Is this exact for everyone?
No. It's an estimate using a single half-life. Your real clearance depends on individual metabolism.
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