Caffeine Half-Life Calculator
See how much caffeine is still in your system at bedtime.
Enter your values
Enter the caffeine consumed in mg.
Enter the hours since consumption in h.
3–4 h for fast metabolisers, 6–9 h if pregnant or on oral contraceptives.
Enter the hours until bedtime in h.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Remaining after 5 h
- 100 mg
- Level at bedtime
- 66 mg
- Time to fall below 50 mg
- 10 h
- Time to fall below 10 mg
- 21.6 h
Above 50 mg can measurably reduce deep sleep.
| Time after dose | Caffeine remaining |
|---|---|
| 0 h | 200 mg |
| 2 h | 151.6 mg |
| 4 h | 114.9 mg |
| 6 h | 87.1 mg |
| 8 h | 66 mg |
| 10 h | 50 mg |
| 12 h | 37.9 mg |
Quick answer
Caffeine has an average half-life of about 5 hours, so half of a 200 mg dose is still circulating 5 hours later and a quarter after 10 hours.
remaining = dose × 0.5^(hours / half-life)
At a glance
| What it does | See how much caffeine is still in your system at bedtime. |
|---|---|
| Category | Health |
| Inputs needed | Caffeine consumed, Hours since consumption, Your half-life, Hours until bedtime |
| Main output | Remaining after 5 h |
| Formula | remaining = dose × 0.5^(hours / half-life) |
| Cost | Free — no sign-up, no download |
How to use the Caffeine Half-Life Calculator
- 1Enter the dose in milligrams (a brewed coffee is roughly 95 mg).
- 2Set your personal half-life.
- 3Check the bedtime level — aim for under 50 mg.
Inputs explained
- Caffeine consumed(mg)
- Enter the caffeine consumed in mg.
- Hours since consumption(h)
- Enter the hours since consumption in h.
- Your half-life(h)
- 3–4 h for fast metabolisers, 6–9 h if pregnant or on oral contraceptives.
- Hours until bedtime(h)
- Enter the hours until bedtime in h.
Worked example
Using the values the calculator loads with:
Inputs
- Caffeine consumed200 mg
- Hours since consumption5 h
- Your half-life5 h
- Hours until bedtime8 h
Results
- Remaining after 5 h100 mg
- Level at bedtime66 mg
- Time to fall below 50 mg10 h
- Time to fall below 10 mg21.6 h
Frequently asked questions
How long does caffeine stay in your system?
With a 5-hour half-life, a 200 mg dose falls to 100 mg after 5 hours, 50 mg after 10 and about 12 mg after 20 hours. Traces can persist for a full day.
How much caffeine is in a cup of coffee?
Roughly 95 mg for an 8 oz brewed coffee, 63 mg per espresso shot, 47 mg for black tea and 80 mg for a standard energy drink.
What do I need to enter into the Caffeine Half-Life Calculator?
Just 4 values: caffeine consumed, hours since consumption, your half-life, hours until bedtime. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Caffeine Half-Life Calculator work out the answer?
Caffeine has an average half-life of about 5 hours, so half of a 200 mg dose is still circulating 5 hours later and a quarter after 10 hours. It applies the formula remaining = dose × 0.5^(hours / half-life) and shows the working so you can check each step by hand.
Is the Caffeine Half-Life Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.