Caffeine Half-Life Calculator

Caffeine has a half-life of about 5.7 hours, so a 200 mg filter coffee at 8am is still leaving roughly 47 mg in your blood at eight in the evening. Add what you drank and when, and this draws the whole curve, stacked drinks included, with the time it falls below 50 mg and 20 mg.

Your Caffeinated Drinks Today

Your Target Bedtime

Caffeine Levels Over Time

Caffeine drops below 20mg at

Optimal bedtime (below 50mg)

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.

How the caffeine curve is calculated

One equation, applied per drink and then added up: the caffeine left from a dose is the dose multiplied by 0.5 raised to the power of the hours elapsed divided by the half-life. The half-life used here is 5.7 hours. So 200 mg — a filter coffee and a bit — taken at 8am is down to about 100 mg by two in the afternoon, about 47 mg by eight in the evening and about 22 mg by two in the morning, and the graph is that curve for every drink summed at each point in the day — which is the reason stacking three drinks keeps the level up far longer than any one of them would.

The two times the tool reports are found by walking forward from your last drink in one-minute steps until the total falls to or below a threshold: 20 mg for "clear" and 50 mg for the suggested bedtime. Those two thresholds are ours. There is no published cut-off for how little caffeine still affects sleep, the effect is dose-dependent and varies hugely between people, and a bedtime warning fires when more than 50 mg is still on board because that is roughly a cup of tea's worth — a figure we chose as a reasonable line, not one anybody publishes.

The half-life is the other figure to hold loosely. Around five to six hours is the range usually quoted for a healthy adult, and individual clearance varies by a factor of several depending on genetics, liver enzymes, smoking, pregnancy and oral contraceptives. Using 5.7 hours for everyone is a simplification, and if caffeine reliably keeps you up longer than this curve suggests, your own half-life is probably the reason rather than the arithmetic. The preset drink strengths — 63 mg for an espresso, 95 for filter coffee, 150 for an Americano, 160 for an energy drink, 40 for tea — are typical figures, not measurements of what you are holding.

Nothing on this site is medically reviewed. Every figure above was read out of the code that runs on this page, and where a number is our own judgement rather than a published one, the note says so and cites nothing. Method last checked 21 August 2026.

Why the afternoon coffee is still with you at midnight

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.