// tool 01 · decay
Caffeine Half-Life Calculator
Enter what you drank and when — this tool shows exactly how much caffeine is still active in your system right now, and when it'll drop low enough to not mess with your sleep.
Half-life varies by genetics, liver function, pregnancy, smoking, and medication — "Average" is a reasonable default for most healthy adults.
What is caffeine half-life?
Caffeine half-life is the time it takes your body to break down and clear half of the caffeine you consumed. For most healthy adults, that's roughly 5 hours — though it can range from 3 to 7 hours depending on genetics, liver function, pregnancy, smoking status, and certain medications.
This means caffeine doesn't just "wear off" — it decays gradually. If you drink a 95mg coffee at 9am, you'd still have around 47mg left at 2pm, and about 24mg by 7pm. That lingering caffeine is often why an afternoon coffee quietly wrecks a night's sleep.
How this calculator works
The calculator uses the standard exponential decay formula used in pharmacology:
Remaining caffeine = Dose × 0.5^(hours elapsed ÷ half-life)
It applies this to the amount and time you enter, then plots the decay curve forward so you can see when your level crosses the 50mg mark — a commonly cited threshold below which caffeine is less likely to disrupt sleep for most people.
Typical caffeine content by drink
| Drink | Typical serving | Caffeine |
|---|---|---|
| Cold brew coffee | 12oz | ~155mg |
| Monster energy | 16oz can | ~160mg |
| Brewed coffee | 8oz cup | ~95mg |
| Sting / generic energy drink | 8oz can | ~92mg |
| Latte / Cappuccino | 8oz, 1 shot | ~77mg |
| Red Bull | 8.4oz can | ~80mg |
| Matcha | 8oz cup | ~70mg |
| Espresso | 1 shot (30ml) | ~63mg |
| Instant coffee | 8oz cup | ~62mg |
| Black tea | 8oz cup | ~47mg |
| Chai tea with milk | 8oz cup | ~40mg |
| Cola soda | 12oz can | ~34mg |
| Green tea | 8oz cup | ~28mg |
| Dark chocolate | 1oz | ~24mg |
| Decaf coffee | 8oz cup | ~3mg |
Frequently asked questions
Why does my half-life matter for sleep?
Caffeine blocks adenosine, the chemical that makes you feel sleepy. As long as a meaningful amount is still active in your system, it can delay sleep onset and reduce deep sleep — even if you don't consciously feel "wired."
Is the 50mg sleep-friendly threshold exact?
No — it's a commonly used reference point, not a hard medical rule. Sensitive individuals may need levels much lower than 50mg before sleep, while regular heavy users may tolerate more. Use it as a general guide, not a guarantee.
Does this account for multiple drinks in one day?
This version calculates one drink at a time. For tracking several drinks across a full day, use the Daily Caffeine Tracker, which adds up overlapping doses as they decay.