Caffeine Calculator
Estimate how much caffeine is still in your system over time using a 5-hour half-life.
Caffeine has a half-life of about 5 hours in a typical adult, so roughly half of it is gone every 5 hours. A brewed cup of coffee has ~95 mg, an energy drink ~80 mg, and a shot of espresso ~63 mg. Below 50 mg most people don't feel a noticeable effect.
Half-life varies a lot with genetics, pregnancy, smoking, and some medications. Estimate only, not medical advice.
How it works
Caffeine leaves your body on an exponential curve. In a typical adult its half-life is about 5 hours, meaning half of whatever you drank is gone every 5 hours. We start from the milligrams you took in and multiply by one-half raised to the power of your elapsed hours divided by 5.
For a sense of scale, a brewed cup of coffee has roughly 95 mg of caffeine, an energy drink about 80 mg, and an espresso shot around 63 mg. Drink 200 mg and three hours later you'll still have about 132 mg circulating.
The tool also solves for when your level falls under 50 mg — the point where most people stop noticing an effect. From a 200 mg dose that happens about 10 hours after your first sip, which is why an afternoon coffee can still nudge your sleep.
Frequently asked questions
Why 5 hours for the half-life?
Five hours is the commonly cited average for a healthy adult. Your own rate varies with genetics, age, liver health, smoking, pregnancy, and certain medications, so treat this as a typical case rather than your exact clearance.
How much caffeine is too much?
Health agencies generally consider up to about 400 mg a day safe for most healthy adults, and less if you're pregnant or sensitive. This calculator shows how a dose fades, not a personal safe limit.
Will this help me sleep better?
It can. If you see you'll still have 50+ mg on board at bedtime, moving your last coffee earlier often helps. It's a guide, not medical advice.