Caffeine Calculator & Half-Life Tracker
Track how caffeine builds, peaks, and clears from your body over time. Enter your dose, drink time, and metabolism speed to see a personalised caffeine curve — including when caffeine drops low enough for quality sleep. Supports multiple doses so you can model a full day's intake.
Your Caffeine Timeline
Based on the caffeine half-life model — C(t) = C₀ × (½)^(t/t½) — this chart shows how caffeine concentration in your bloodstream rises with each dose and decays over time. Results update automatically as you adjust inputs above.
Will This Affect Your Sleep?
Caffeine blocks adenosine receptors — the chemical that makes you feel tired. Even when you no longer feel alert, residual caffeine can reduce sleep quality, shorten deep sleep stages, and delay sleep onset. The threshold used here is 25 mg remaining, below which sleep impact is considered minimal for most adults.
Calculate above to see your sleep impact.
General sleep hygiene tips for caffeine users
- Most adults should stop caffeine intake 6–8 hours before their target bedtime
- Caffeine sensitivity increases with age — older adults may need a longer buffer
- Alcohol does not counteract caffeine; both can independently disrupt sleep architecture
- Morning caffeine (before noon) has the least impact on evening sleep quality
How Long Does Caffeine Last? (By Dose)
Caffeine doesn't disappear instantly. Its effects depend on dosage and your body's metabolism speed. The table below is a general reference based on an average 5-hour half-life for a healthy adult. Actual clearance times vary with age, liver function, medications, and genetics.
| Caffeine dose | 50% cleared (half-life) | 25% remaining | Mostly cleared |
|---|---|---|---|
| 50 mg | 3–4h | 6–8h | 8–10h |
| 100 mg | 4–5h | 8–10h | 12–14h |
| 200 mg | 5–6h | 10–12h | 15–18h |
| 300 mg | 5–7h | 10–14h | 18–22h |
| 400 mg | 6–8h | 12–16h | 20–24h |
Caffeine can remain detectable in your system for up to 24 hours at higher doses or for individuals with slower metabolism. The values above assume a normal adult metabolism with no significant drug interactions. Oral contraceptives, some antibiotics, and liver conditions can extend caffeine half-life significantly.
Common Caffeine Amounts in Drinks
Wondering how much caffeine is in your favourite order? Here are some of the highest-caffeine drinks from the brands covered on this site. Click any card to see the full nutrition breakdown including caffeine by size, sleep cut-off times, and keto suitability.
What This Means for You
Based on your inputs, here's a personalised summary of your caffeine situation — including timing recommendations and what to watch out for.
Calculate your caffeine timeline above to see personalised insights here.
Caffeine FAQ
Common questions about caffeine metabolism, safe intake levels, and how caffeine interacts with sleep.
Caffeine has a half-life of 3–7 hours in most healthy adults, meaning it takes that long for half the caffeine to be eliminated. A standard 200 mg dose can take 12–18 hours to fall below 10% of the original amount. At higher doses (300–400 mg), trace amounts may remain active for up to 24 hours.
The FDA advises healthy adults to stay under 400 mg of caffeine per day — roughly equivalent to four 8-oz cups of brewed coffee. Consuming 1,200 mg or more in a short period can cause toxic effects. For pregnant individuals, the recommended limit is 200 mg/day. Adolescents should stay under 100 mg/day.
Yes. Even when you no longer feel alert, caffeine continues to occupy adenosine receptors in the brain. Research shows that caffeine consumed 6 hours before bedtime can reduce total sleep time by more than one hour. The effect is more pronounced in people with slower metabolism or higher sensitivity.
Caffeine is primarily metabolised by the liver enzyme CYP1A2. In most adults, the half-life is 5 hours — meaning 50% is cleared every 5 hours. This rate varies significantly: smokers metabolise caffeine roughly twice as fast; pregnant individuals and those on certain medications (like some oral contraceptives) metabolise it two to three times more slowly.
Yes — in both directions. Regular consumption builds tolerance, reducing the alertness effect but not necessarily the sleep-disrupting effect. Caffeine sensitivity also tends to increase with age as metabolism slows. Taking a break of several days resets tolerance, at which point lower doses produce stronger effects.