Caffeine Half-Life Calculator

Your drinks today

Metabolism speed (caffeine half-life)

5.0 h

Faster: smoking. Slower: oral contraceptives, pregnancy, some medications, and liver conditions. Genetics matter too.

Bedtime

Times before 4 AM count as the following night.

At bedtime

-- mg

Peak level

-- mg

Drops below 50 mg

About half a cup of coffee's worth

Mostly cleared

Below 10 mg, roughly a cup of decaf

Caffeine in your body

Tap or hover the chart to read levels

Caffeine (mg) Bedtime 50 mg line Drink

How it works

Each drink is absorbed over roughly the first hour, then cleared by your liver at a steady proportional rate. Every half-life, half of what's left is gone. The calculator adds up every drink's curve to get your total.

A(t) = Σ D_i · k_a / (k_a − k_e) · ( e^−k_e·Δt − e^−k_a·Δt )
k_e = ln 2 / t_½ · k_a ≈ 4 per hour · Δt = hours since drink i

Assumptions

A one-compartment model with first-order absorption, which puts each drink's peak about 45–60 minutes after drinking.
Nearly all ingested caffeine is absorbed. The drink amount is treated as the dose.
Half-life is constant over the day. In reality, very high intake can slow clearance a bit.
Caffeine content varies widely by brand, roast and brew. The presets are typical values; edit the mg to match your drink.
"Sleep impact" is a rough guide. Tolerance and individual sensitivity vary a lot.

Sources

Institute of Medicine (2001). Caffeine for the Sustainment of Mental Task Performance. National Academies Press.
Nehlig, A. (2018). Interindividual differences in caffeine metabolism and factors driving caffeine consumption. Pharmacological Reviews, 70(2).
Drake, C. et al. (2013). Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed. Journal of Clinical Sleep Medicine, 9(11).
USDA FoodData Central, for typical caffeine content of beverages.