CaffCalc

The caffeine calculator

Caffeine, beyond
the last sip.

See how your coffee, tea and energy drinks add up—and what may remain at bedtime.

Calculate my caffeine Explore the drinks
  • No account needed
  • No pre-filled drinks
  • Adjustable half-life

An estimate, not a measurement or sleep prediction. How it works

AI-generated editorial illustration of coffee, tea and a clock on a sunlit table.
A sip can linger.Half-life example
An illustrative caffeine timelineA 100 milligram dose with a five-hour half-life decreases to 50 milligrams after five hours and 25 after ten. This is an example, not your result.
At the start
100 mg
After 5 hours
50 mg
After 10 hours
25 mg

Illustration using a 5-hour half-life. Your clearance rate may differ.

Your day, in milligrams

Put your drinks on a timeline.

Add a drink. Choose bedtime.
Explore what might remain.

Step 1

Your drinks

Common drink shortcuts

Compare servings and sources
Start with what you drankChoose a shortcut, browse the sourced database, or add a custom drink from its label.
Step 2

Bedtime and calculation

A 5 hour half-life is a common estimate, but metabolism varies by person.

Add at least one drink to continue.

Choose by question

What are you trying to work out?

Build a coffee-shop orderChoose Starbucks or Costa servings, sizes and extra-shot estimates.What can I drink now?Find servings that fit your chosen bedtime caffeine target.Find a lower-caffeine swapCompare alternatives to your usual drink by brand and category.Track your caffeineLog favourites in a tap and explore your weekly patterns.
See every caffeine tool

How the estimate works

Caffeine wears off gradually, not all at once. With a five-hour half-life, 100 mg falls to about 50 mg after five hours, 25 mg after ten hours and 12.5 mg after fifteen hours. We work out an estimate for each drink, then add them up at your chosen bedtime.

Your body may clear caffeine faster or slower. Pregnancy, medicines, smoking, liver function and genetics can all make a difference. That’s why we show several half-life examples rather than pretending one setting fits everyone. See how the calculation works.

How to use the result

Start with your usual day. Then try moving your last drink earlier, choosing a smaller serving or making a lower-caffeine swap. Compare the results to see what changes. Remember to include tea, cola, energy drinks and caffeinated pre-workout as well as coffee—earlier drinks may still contribute at bedtime.

The 50 mg, 25 mg and 10 mg markers help you follow the curve. They aren’t proven safe levels or guarantees of good sleep. Feeling less awake doesn’t mean all the caffeine has gone, either. For examples, see when to stop caffeine before bed or try the caffeine planner.

A few things to keep in mind

This is an estimate, not a test of the caffeine in your body. Drink amounts and people’s responses vary, so the result can’t predict your sleep or replace medical advice. Check your current product label and try different half-life settings to see a range of possibilities.

If you have chest pain, a racing or irregular heartbeat, severe anxiety, vomiting or other worrying symptoms after caffeine, seek medical help. If you’re pregnant, take medicines, have a health condition or keep having trouble sleeping, ask a qualified healthcare professional for personal advice. Our sources page explains where the site’s information comes from.

Caffeine calculator FAQ: how long caffeine lasts, sleep, and half-life

Answers to common questions about how long caffeine stays in your system, caffeine half-life, caffeine before bed, and how to use a caffeine calculator.

Caffeine can stay in your system for several hours or even most of the day. For many adults, the caffeine half-life is around 5 hours, meaning about half of the caffeine may still be in your body after that time. But it can take 10 hours or more for caffeine to be mostly cleared, depending on metabolism, genetics, and other factors.