What's the typical caffeine half-life?

About 5 hours in healthy adults (range 1.5-9.5 hours). Half-life means: every 5 hours, the amount in your bloodstream drops by 50%. So 200 mg at 9 am becomes ~100 mg at 2 pm, ~50 mg at 7 pm, ~25 mg at midnight.

What slows caffeine clearance?

Pregnancy (extends half-life to 10-20 hours, especially in third trimester), oral contraceptives (~doubles half-life), liver disease, certain antibiotics (ciprofloxacin), genetic variations in CYP1A2 (the enzyme that metabolises caffeine — 'slow metabolizers' may have 7-9 hour half-life).

Smoking (induces CYP1A2, halves the half-life to ~2.5 hours — quitters often report increased caffeine sensitivity for weeks), some anti-seizure medications.

How much caffeine is in common drinks?

Espresso shot: ~63 mg · Drip coffee 8 oz: ~95 mg · Brewed black tea 8 oz: ~47 mg · Green tea 8 oz: ~28 mg · Coca-Cola 12 oz: ~34 mg · Red Bull 8.4 oz: ~80 mg · Energy shot 2 oz: ~200 mg.

When should I stop drinking caffeine before bed?

Sleep researchers commonly recommend ≥6-8 hours before bedtime. With a 5-hour half-life, a 200 mg dose at 2 pm leaves ~50 mg at 9 pm and ~25 mg at 2 am — enough to fragment sleep architecture in many people. Test your own threshold by comparing sleep quality on caffeine-free days.

Is this calculator medical advice?

No. It's a first-order kinetic model using population averages. Individual half-life varies 6-fold. Pregnant people, those on medications, or anyone with sleep concerns should consult a doctor.

Caffeine Half-Life Calculator

Health & Fitness· 18 tools

Free caffeine half-life calculator. Caffeine clearance follows first-order kinetics with a typical adult half-life of about 5 hours (range 1.5-9.5 hours). Enter dose, intake time, and any individual factors (pregnancy, smoking, oral contraceptives) to project the caffeine remaining at any future time. Useful for planning sleep — most sleep researchers recommend caffeine drop below 50 mg before bedtime.

Caffeine dose (mg)

Intake time

Check time

Half-life (hours)

Formula · remaining = dose × 0.5^(hours / half-life)

Half-life: 5h healthy adult · 10–20h pregnant · ~10h on oral contraceptives · ~2.5h smoker

Quick presets

Remaining at 23:00

28.7 mg

14% of dose · +14h 0m elapsed

Drops below 50 mg

+10h 0m (19:00)

≤1 mg cleared

+38h 13m

After 1 half-life (5h)100.0 mg

After 2 half-lives (10h)50.0 mg

After 3 half-lives (15h)25.0 mg

Disclaimer: For informational purposes only. This is not medical advice — consult a qualified healthcare provider for personal recommendations.

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