Skip to main content
BeHabitual

Sleep and time

Caffeine half-life calculator

A 3pm coffee is not gone by 10pm. This shows how much is still there.

By Nabeel Mustafa. Updated .

Runs in your browser. Nothing is sent, saved, or shared.

mg

95 mg is a typical 8-ounce drip coffee

8 hrs

From the last sip

5 hrs

Typical is 5. Usual range is 3 to 7

Still in your system

31 mg

Dose times one-half to the power of hours over half-life

Starting dose
95 mg
Half-lives elapsed
1.6

Remaining milligrams are not a verdict on whether you will sleep. Sensitivity varies enough that the same leftover keeps one person up and leaves another person fine. Use last week of sleep as the check, not this number alone.

A timer runs the session. Whether the sessions happen most days is a different record: a free habit tracker that shows the whole month on one screen.

Track it as a habit

The number this uses, and the range it hides

Typical half-life in healthy adults is about 5 hours. That is the figure most references quote, and it is the default here. The range is roughly 3 to 7 hours, which is why the field is editable. A 3-hour half-life and a 7-hour half-life on the same 200 mg dose are not the same evening.

Pregnancy, smoking, and some medications change the clearance a lot. This page cannot see any of that. If you are in one of those groups, treat the result as a sketch and talk to a doctor before you use it to time a last cup.

What remaining milligrams actually mean

Half-life means the amount halves every N hours, not that it vanishes at N. Two half-lives leave a quarter. Four leave a sixteenth. A 200 mg coffee at 2pm, with a 5-hour half-life, still has about 50 mg in you at midnight. That is not nothing.

The page will not tell you a remaining amount that is 'fine to sleep on'. Sensitivity varies enough that a number which leaves one person asleep keeps another person counting ceiling tiles. Read the milligrams, then use your own last week of sleep as the check.

A 95 mg default, and why yours may differ

The starting dose is 95 mg, a typical 8-ounce drip coffee. Espresso, energy drinks, and tea sit somewhere else, and a large mug is not 8 ounces. Type the serving you actually drank. Stacking two cups means adding the milligrams, not running the tool twice and hoping.

Estimate what is left at bedtime

  1. Enter the milligrams

    95 is a typical 8-ounce drip coffee. Check the can or the shop if you can; guesses compound.

  2. Enter hours until you want to sleep

    From the last sip, not from when you sat down with the cup.

  3. Leave half-life at 5 unless you have a reason

    The usual range is 3 to 7 hours. Move it only if you already know you clear caffeine unusually fast or slowly.

  4. Read remaining milligrams, not a verdict

    The tool will not tell you whether you will sleep. It tells you what is still there.

Questions people ask

What is the half-life of caffeine?

About 5 hours in healthy adults, with a usual range of roughly 3 to 7 hours. Pregnancy and some medications can push it well outside that range.

How much caffeine is left after 8 hours?

On a 5-hour half-life, a bit more than a quarter of the original dose. 200 mg at noon is still about 66 mg at 8pm.

When should I stop drinking coffee?

Work backwards from bedtime using this page. If 50 mg still keeps you up, you need more hours than someone who sleeps through 80. The cutoff is personal; the remaining milligrams are not.

Does this count tea and energy drinks?

Yes, if you type their milligrams. The half-life is a property of caffeine, not of coffee. A 150 mg energy drink and a 150 mg coffee leave the same amount behind.

Other tools

Read next

Numbers are easy. Doing it every day is the hard part.

A calculator tells you where you are once. If the thing you actually want is to keep something up, that takes a record rather than a result.

Start trackingSee how it works