Caffeine Calculator See How Long Caffeine Stays In Your System
- LIVE MODEL
- HALF-LIFE ~5.0h
- 1 CUP ~95mg
- CLEARS IN ~50h
How Long Does a Specific Dose of Caffeine Last?
A dose of caffeine does not vanish all at once. It halves about every 5 hours on average, then tapers off slowly. Here is roughly how long common amounts stay active at a typical 5 hour half-life.
Caffeine Duration Chart
| Caffeine dose | After 5 hrs | After 10 hrs | Sleep-safe (under 12 mg) |
|---|---|---|---|
| 50 mg | 25 mg | 12 mg | about 10 hrs |
| 100 mg | 50 mg | 25 mg | about 15 hrs |
| 150 mg | 75 mg | 38 mg | about 18 hrs |
| 200 mg | 100 mg | 50 mg | about 20 hrs |
| 300 mg | 150 mg | 75 mg | about 23 hrs |
| 400 mg | 200 mg | 100 mg | about 25 hrs |
Quick Dose Calculator
Just for fun, not medical advice. This uses a simplified first-order decay model at your chosen half-life. Real caffeine peaks 30 to 45 minutes after drinking and clears at a rate that varies with genetics, medication, pregnancy, and liver health.
Good to Know
Caffeine Questions, Answered
Straight answers on caffeine half-life, how long a dose lasts, sleep, and safe limits. Run your own numbers in the calculator above.
Caffeine Half-Life
The half-life is the time your body takes to clear half of the caffeine you drank. For most healthy adults it is about 5 hours, with a range of roughly 3 to 7 hours. So a 100 mg coffee drops to about 50 mg after 5 hours and about 25 mg after 10. You can model your own curve in the caffeine calculator above.
I use a simple first-order decay model. You add your drinks and set your half-life, and the tool halves the caffeine once every half-life cycle to draw how much is left over time. It assumes caffeine is absorbed quickly, so the earliest readings are approximate.
Half-life varies with genetics, liver function, medication, and pregnancy. A fast metabolizer clears a dose in about 3 hours per cycle, while a slow metabolizer can take 8 hours or more. Slide your own half-life in the calculator to see how it reshapes the curve.
How Long Caffeine Lasts
Caffeine fades on a curve set by its half-life, about 5 hours for most people. Half is gone after one half-life and a quarter after two. A dose usually drops below a level you can feel after about 4 to 5 half-lives, which can be 20 hours or more for a large amount.
At a 5 hour half-life, about 50 mg is left after 5 hours and 25 mg after 10. It falls below a sleep-safe level, under about 12 mg, after roughly 15 hours. A fast metabolizer clears it sooner.
About 100 mg is still active after 5 hours and 50 mg after 10. It reaches a sleep-safe level after roughly 20 hours, which is why a mid-afternoon energy drink can still affect sleep that night.
A common rule is to stop about 8 hours before bed, though it depends on the dose and your half-life. Set your target bedtime in the calculator and it shows how much caffeine is still active when you try to sleep.
Caffeine & Sleep
Yes. Because caffeine lingers for hours, a late dose keeps a measurable amount in your system at bedtime, which can delay sleep and cut into deep sleep. The calculator shows your estimated level at your chosen bedtime.
It depends on how much you drank, when you drank it, and your half-life. Add your drinks and set your bedtime in the tool above, and it reports the milligrams still active when your head hits the pillow.
How Much Caffeine
The U.S. Food and Drug Administration points to 400 mg per day as an amount not generally linked to negative effects for healthy adults. That is roughly four 8 ounce cups of brewed coffee. Pregnant people and those sensitive to caffeine should aim much lower.
A brewed 8 ounce coffee has about 96 mg, a single espresso about 64 mg, a double about 128 mg, cold brew about 155 mg, and a 16 ounce energy drink about 160 mg. The full list of drink values sits inside the calculator above.
Weight does not change how fast you clear caffeine, so your half-life stays the same. What it changes is concentration. The same dose is more concentrated in a smaller person, which the calculator reports as your peak blood level in mg per liter.
By weight they are very close. Measured by scoop, light roast can have a touch more because the beans are denser. Roast level changes flavor far more than it changes caffeine.