What is caffeine half-life?

Half-life is the time for your body to eliminate half the caffeine in your system. For most healthy adults this is roughly 5–6 hours (mean ~5.7 h). The amount remaining follows exponential decay: C(t) = C0 × 0.5^(t / t_half).

Why does the calculator let me change the half-life?

Metabolism varies widely. Smokers clear caffeine roughly twice as fast (~3.5 h half-life). Pregnancy and hormonal contraceptive use can extend it to ~10 h. Liver disease and some medications also affect clearance.

What sleep threshold should I use?

Research suggests most people can fall asleep when blood caffeine is below 50–100 mg. The default of 50 mg is conservative. If you are caffeine-sensitive, lower it; if you routinely sleep fine with caffeine, you can raise it.

Why does the chart only go to 24 hours?

Caffeine from a single dose is essentially gone within 24 hours for nearly all realistic inputs. The chart covers the full day from consumption time so you can see the entire trajectory.

Is this medically accurate?

The formula is pharmacokinetically standard, but actual clearance depends on many individual factors. Use this as a rough guide, not a clinical tool.

Caffeine Half-Life Calculator

Name: Caffeine Half-Life Calculator
Availability: InStock
Author: Nham Vu

Enter your caffeine intake and consumption time to see how much is left in your system and when you can sleep.

Caffeine Inputs

Caffeine amount (mg)

Espresso (1 shot) ~63 mg Drip coffee (8 oz) ~95 mg Energy drink ~80–160 mg Black tea (8 oz) ~40–70 mg Green tea (8 oz) ~25–45 mg Cola (12 oz) ~35 mg

Time consumed

Current time

Half-life: 5.7 hours

3 h (smokers) 5.7 h (average) 9 h (slow)

Pregnancy / hormonal contraceptives: ~10 h (slide to max as approximation).

Sleep threshold (mg)

Caffeine below this level is unlikely to disrupt sleep for most people.

Caffeine right now

—

Safe to sleep

—

24-hour decay curve

Alert (>100 mg) Moderate (50–100 mg) Sleep-safe (<50 mg)

Formula

Remaining caffeine: C(t) = C0 × 0.5^(t / t_half)

Time to sleep threshold: t = t_half × log2(C0 / threshold)

Summary

Enter your caffeine intake and consumption time to see how much is left in your system and when you can sleep.

How it works

Enter the amount of caffeine in milligrams (use the reference table for common drinks).
Set the time you consumed the caffeine using the clock input.
Adjust the half-life slider if you have personal factors (smokers metabolize faster; pregnancy and hormonal contraceptives slow it down).
Set the sleep threshold — caffeine below this level is unlikely to disrupt sleep for most people.
The chart and summary update instantly, showing current caffeine level and when it drops below your threshold.

Use cases

Plan your last coffee of the day so it does not interfere with sleep.
Understand why an afternoon energy drink keeps you awake at midnight.
Gauge how long a large pre-workout dose will stay active.
Compare sleep readiness between a light tea and a double espresso.

Frequently Asked Questions

Last updated: 2026-07-23 · Reviewed by Nham Vu