Caffeine Half-Life Calculator

See exactly when caffeine leaves your system and whether it's affecting your sleep.

Your Caffeinated Drinks Today

Your Target Bedtime

Caffeine Levels Over Time

Caffeine drops below 20mg at

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Optimal bedtime (below 50mg)

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Half-life used: ~5.7 hours (average adult). Actual half-life varies by genetics, age, and medications. Smokers metabolize caffeine faster (~3 hours), while pregnant women metabolize it slower (~11 hours). Oral contraceptives can also double the half-life.

Why This Matters

Caffeine is the world's most widely consumed psychoactive substance, and most people have no idea how long it actually stays in their system. That 3pm "pick-me-up" coffee? Half of it is still circulating in your blood at 9pm.

The half-life model is simple but powerful. Caffeine follows predictable exponential decay in the body. With a half-life of approximately 5.7 hours, a 200mg dose (typical filter coffee) at 8am leaves about 100mg at 2pm, 50mg at 8pm, and 25mg at 2am. That last 25mg — equivalent to half a cup of tea — can still measurably disrupt your sleep architecture.

What makes this calculator useful is stacking. Most people don't drink just one coffee. A morning espresso at 7am plus a latte at 11am plus an afternoon pick-me-up at 3pm creates overlapping decay curves that keep caffeine levels elevated much longer than any single drink would.

The visual graph in this tool shows your real caffeine level throughout the day based on exactly what you consumed and when. For many people, seeing the curve stay elevated well past their bedtime is a wake-up call about why they're not sleeping well.

Frequently Asked Questions

What is the half-life of caffeine?

The average half-life of caffeine in healthy adults is about 5-6 hours, meaning half the caffeine you consumed is still in your system 5-6 hours later. However, this varies significantly based on genetics, age, liver function, pregnancy, and medications.

How much caffeine is in common drinks?

An espresso shot contains about 63mg, filter coffee about 95mg, a large Americano about 150mg, energy drinks around 160mg, and tea about 40mg. These are averages — actual amounts vary by brand, brewing method, and serving size.

When should I stop drinking coffee before bed?

As a general rule, stop consuming caffeine 8-10 hours before your target bedtime. For a 10pm bedtime, that means no caffeine after noon-2pm. Even if you "can fall asleep" after late coffee, research shows caffeine still disrupts deep sleep quality.

How does caffeine affect sleep?

Even 200mg of caffeine (about 2 cups of coffee) consumed 6 hours before bed can reduce total sleep time by over an hour and significantly decrease deep sleep. Caffeine blocks adenosine receptors, which are critical for sleep drive.