Caffeine Half-Life Calculator (How Much Is Still in Your Body?)

What this tool does

Caffeine fades exponentially: every half-life removes half of what is left, so a 200 mg coffee leaves roughly 100 mg five hours later and 50 mg after ten. The half-life is commonly reported as about 5 hours in a healthy adult, but anywhere from roughly 3 to 7 hours is normal; it is longer in pregnancy, with some medicines and with liver disease, and shorter in smokers. The model treats one dose absorbed quickly, so several cups are best entered one at a time. A cup of brewed coffee often holds somewhere around 80–100 mg, an espresso 60–80 mg and a can of cola 30–40 mg, but brands vary a lot.

Formula

C = C₀ × ½^(t ÷ t½) · t = t½ × log₂(C₀ ÷ C)

Variables

Symbol	Meaning	Unit
`d`	Caffeine in the drink	mg
`t`	Hours since you drank it	h
`hl`	Your caffeine half-life (about 5 h for most adults)	h
`th`	Level you are happy to go to bed with	mg
`R`	Caffeine still in your body	mg
`P`	That is this share of the dose	%
`TT`	Hours from now until it drops to that level	h
`HL`	Half-lives elapsed	—

Worked example

Caffeine in the drink200 mg
Hours since you drank it6 h
Your caffeine half-life (about 5 h for most adults)5 h
Level you are happy to go to bed with50 mg

Caffeine still in your body87.1 mg
That is this share of the dose44 %
Hours from now until it drops to that level4.0 h
Half-lives elapsed1.20

Limitations

This tool is informational only. It does not diagnose, treat or replace a qualified health professional. Speak to a doctor before making decisions about your health.
The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.