What is the half-life of caffeine?

The average half-life of caffeine in healthy adults is about 5 hours, meaning half the caffeine you consumed is still active after 5 hours. However, this varies significantly between individuals — from 1.5 to 9.5 hours — depending on genetics (CYP1A2 enzyme), liver function, medications, pregnancy, and smoking status.

How much caffeine is in common drinks?

Typical amounts: espresso shot 63mg, drip coffee (8oz) 95mg, cold brew (16oz) 200mg, energy drink 160mg, green tea 28mg, black tea 47mg, pre-workout supplement 200mg, cola/soda 40mg. Actual amounts vary by brand and preparation.

When should I stop drinking caffeine to sleep well?

A common guideline is to stop caffeine 8-10 hours before bedtime. This calculator shows you exactly when caffeine from your last drink drops to negligible levels. Even small amounts (under 25mg) can affect sleep quality in sensitive individuals.

Does caffeine tolerance affect half-life?

Tolerance affects how strongly you feel the effects but does NOT significantly change the half-life. Regular consumers may not feel jittery at levels that would overstimulate a novice, but the caffeine persists in their system just as long.

What factors speed up or slow down caffeine metabolism?

Faster: smoking (halves the half-life), cruciferous vegetables, certain medications. Slower: pregnancy (doubles the half-life), oral contraceptives, liver disease, CYP1A2 slow-metabolizer genetics. Some people are genetically "fast metabolizers" and clear caffeine in 2-3 hours.

Caffeine Half-Life Calculator

See how much caffeine remains in your system hour by hour, and when it will clear below the threshold that affects sleep.

Calculator

How Caffeine Decay Works

Caffeine follows first-order elimination kinetics — it decays exponentially, not linearly. This means a fixed percentage (not a fixed amount) is eliminated each hour. The half-life determines how quickly: with a 5-hour half-life, 200mg becomes 100mg at 5h, 50mg at 10h, 25mg at 15h, and so on.

Caffeine and Sleep

Caffeine blocks adenosine receptors, preventing the "sleepy signal" from accumulating. Even when you no longer feel alert, residual caffeine can reduce deep sleep (NREM Stage 3) duration and delay sleep onset. Studies show that caffeine consumed 6 hours before bed can reduce total sleep time by over an hour.

Formula

Remaining caffeine = Initial dose × (0.5)^(hours / half-life)

Common Caffeine Sources

SourceCaffeine (mg)

Espresso (1 shot)63

Drip Coffee (8 oz)95

Cold Brew (16 oz)200

Energy Drink160

Green Tea28

Black Tea47

Pre-Workout200

Soda/Cola40

Tips & Limitations

Stop caffeine 8-10 hours before bedtime for optimal sleep quality

Caffeine takes 30-60 minutes to reach peak blood levels

If you are pregnant, your half-life roughly doubles — consult your doctor about limits

Smoking accelerates caffeine metabolism by ~50%

Pair caffeine with L-theanine (found in tea) for smoother alertness without jitters

Medical Disclaimer

This calculator provides estimates based on average caffeine metabolism. Individual variation is significant. If you are sensitive to caffeine, pregnant, or taking medications that affect liver enzymes, consult your healthcare provider.