Caffeine Calculator: How Much Is Left in You at Bedtime?

Caffeine Calculator: When Will Caffeine Wear Off?

Add each coffee, tea or energy drink and the time you had it to see how much caffeine is still in your system at bedtime. It also shows when you drop below a level that lets most people sleep, and you can adjust the half-life if caffeine hits you harder or lighter than average.

By Suman Sharma · Updated October 25, 2026

How to use this tool

Add your drinks

Pick each drink from the list, or type a custom amount from the label, and set the time you finished it.

Set your bedtime

Enter when you plan to go to sleep. A time after midnight is counted as the next morning.

Read the result

See the caffeine left at bedtime, when it falls below your target, and a chart of the whole day.

Example

A morning coffee and a big afternoon one, with an 11 PM bedtime.

Input

8:00 AM: brewed coffee, 95 mg
2:00 PM: large coffee-shop coffee, 300 mg
Bedtime: 11:00 PM · Half-life: 5 hours

Result

Caffeine at bedtime: 98 mg
Falls below 50 mg at 3:52 AM
Total for the day: 395 mg, within the 400 mg guideline
Swap the afternoon cup for a regular coffee at noon: 33 mg at bedtime

The afternoon cup matters far more than the morning one. With a 3-hour half-life the same day leaves 40 mg at bedtime; with 7 hours, 145 mg.

How long caffeine lasts

Caffeine is absorbed within about an hour and then broken down by the liver at a steady rate. The time it takes your body to clear half of it is its half-life. For most healthy adults that's around 5 hours, but it ranges widely, from roughly 1.5 to 9.5 hours.

So if you drink 200 mg at 2 PM, about 100 mg is left at 7 PM and about 57 mg at 11 PM. Every drink follows its own curve, and they stack: an afternoon coffee lands on top of whatever's left from the morning.

What changes your half-life

Smoking: speeds clearance up, roughly halving the half-life.
Pregnancy: slows it down sharply, to as long as 15 hours late in pregnancy.
Oral contraceptives and some medications: can roughly double it.
Liver conditions: slow it down.
Genetics: some people are naturally fast or slow metabolizers.

How much is too much

The US FDA and the European Food Safety Authority both say up to 400 mg a day is not generally associated with harmful effects for healthy adults. EFSA adds that single doses up to 200 mg are fine, and advises up to 200 mg a day during pregnancy. Sensitivity varies a lot, so if caffeine makes you anxious or keeps you up, less is the right amount for you.

This calculator is an estimate for planning, not medical advice.

Caffeine in common drinks

Typical amounts, from USDA data and manufacturers' labels. Coffee in particular varies a lot by bean, brew and cup size.

Brewed coffee, 8 fl oz (240 ml): about 95 mg
Espresso, single shot: about 63 mg
Instant coffee, 8 fl oz: about 60 to 80 mg
Decaf coffee, 8 fl oz: about 2 to 15 mg
Black tea, 8 fl oz: about 47 mg
Green tea, 8 fl oz: about 28 mg
Cola, 12 fl oz can: about 30 to 40 mg
Red Bull, 8.4 fl oz can: 80 mg
Large energy drinks, 16 fl oz: often 150 to 300 mg
Dark chocolate, 1 oz: about 12 to 25 mg

Caffeine and sleep

You don't have to feel wired for caffeine to hurt your sleep. In a 2013 study in the Journal of Clinical Sleep Medicine, 400 mg of caffeine taken six hours before bed cut total sleep by more than an hour, even though many participants didn't notice the difference.

Caffeine works by blocking adenosine, the chemical that builds up during the day and makes you sleepy. While it's still in your blood, you tend to fall asleep later and get less deep sleep. That's why this calculator looks at what's left at bedtime, not just when you had your last cup.

Common errors

Underestimating coffee-shop sizes

A large brewed coffee from a chain can have 300 mg or more, three times a home cup. Check the chain's nutrition page and enter the real figure.

Forgetting hidden caffeine

Pre-workout, cola, iced tea, dark chocolate and some painkillers add up. Add them as custom amounts.

Using the time you started the drink

Enter when you finished it, especially for a coffee you sip over an hour. That's closer to when the caffeine is absorbed.

Assuming decaf is caffeine-free

Decaf coffee still has a little, typically a few milligrams a cup. It only matters if you drink several late in the day.

Frequently asked questions

How long does caffeine stay in your system?

With a typical 5-hour half-life, half is gone after 5 hours and about a quarter remains after 10. It takes roughly 25 hours to clear almost all of it, though most people stop noticing it long before that.

When should I stop drinking coffee before bed?

For many people, around 8 to 10 hours before bed, but it depends on how much you drink and how fast you clear it. Enter your drinks and bedtime to see your own cut-off.

How much caffeine is in a cup of coffee?

About 95 mg in an 8 fl oz (240 ml) cup of brewed coffee and about 63 mg in a single espresso shot. Coffee-shop sizes and cold brew can be much stronger.

How much caffeine is safe per day?

Up to 400 mg a day for most healthy adults, according to the FDA and EFSA, with up to 200 mg a day advised during pregnancy. Some people feel effects at much lower amounts.

How long does it take for caffeine to kick in?

It starts within about 15 to 45 minutes and usually peaks between 30 minutes and 2 hours after you drink it, depending on what else is in your stomach.

Does decaf coffee have caffeine?

A little. An 8 fl oz cup of decaf usually has about 2 to 15 mg, compared with about 95 mg in regular brewed coffee.