Caffeine Half-Life Calculator
See exactly how much caffeine is still in your system right now — and when it will be low enough for a good night's sleep. Enter your dose, time since consumption, and half-life to get remaining caffeine, a full hourly decay timeline, and a sleep safety indicator.
Enter your caffeine details
Enter your caffeine dose, how long ago you had it, and which half-life estimate to use. The typical range for healthy adults is 4–6 hours.
Decay formula
Remaining = Dose × (½)^(t ÷ half-life)
At exactly 1 half-life: 50% remains
At 2 half-lives: 25% remains
At 3 half-lives: ~12.5% remains
Half-life varies widely
Healthy adult: 4–6 hrs (avg ~5)
Heavy smoker: 2–3 hrs (faster)
Pregnancy (3rd trimester): 10–15 hrs
Oral contraceptives: ~6–8 hrs
Liver disease: up to 96 hrs
Common caffeine sources — dose reference
| Source | Typical amount | Caffeine (mg) |
|---|---|---|
| Espresso (single shot) | 30 ml | 60–75 |
| Drip coffee (medium) | 240 ml | 85–120 |
| Drip coffee (large) | 480 ml | 150–200 |
| Cold brew concentrate | 240 ml | 150–250 |
| Black tea | 240 ml | 40–70 |
| Green tea | 240 ml | 25–45 |
| Energy drink (standard) | 250 ml | 80–100 |
| Energy drink (large) | 480 ml | 140–200 |
| Pre-workout (single scoop) | — | 150–300 |
| Dark chocolate (50 g) | 50 g | 25–50 |
Frequently asked questions
What is caffeine half-life?
Caffeine half-life is the time it takes for the concentration of caffeine in your body to reduce by half. After one half-life, 50% remains. After two, 25%. After three, about 12.5%. The commonly cited estimate for healthy adults is around 5 hours, but this varies widely between individuals.
What is a normal caffeine half-life?
For healthy non-pregnant adults, the range is typically 4–6 hours with an average around 5 hours. Smokers tend to metabolise caffeine faster (2–3 hours). Pregnant women in the third trimester metabolise caffeine much more slowly (10–15 hours). Certain medications and liver conditions can also significantly alter the rate.
How much caffeine is safe before bed?
Research suggests that caffeine levels above 25–50 mg at bedtime can reduce sleep quality even if you do not feel alert. This calculator's sleep safety indicator flags when remaining caffeine at your bedtime exceeds 50 mg. The exact threshold varies by individual sensitivity.
Why does caffeine affect people differently?
Differences in the CYP1A2 enzyme activity determine how quickly your liver processes caffeine. Genetics, age, medications (especially contraceptives and some antibiotics), pregnancy, smoking, and liver function all influence the rate. Two people with the same dose can have very different caffeine levels hours later.
Can I use this to plan my coffee timing?
Yes — this is one of the most practical uses. If you know your typical bedtime and rough half-life, you can work backwards to find the latest time a given dose would leave you below 50 mg at sleep time. The hourly schedule table in the results makes this easy to read off directly.
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