Caffeine Calculator: how much is still in you at bedtime?
Estimate the caffeine left in your body when you go to bed, and find your last-call time for coffee, tea, or energy drinks.
How the estimate works
Caffeine leaves your body roughly exponentially. After one half-life, half is left; after two, a quarter, and so on. We compute the amount remaining at your bedtime and the latest time a drink can be finished for the remainder to fall to your chosen bedtime target.
The bedtime target is only a calculation setting. Individual sensitivity varies a lot, and no amount of remaining caffeine is guaranteed to be free of effects on sleep.
Typical caffeine amounts
| Drink | Caffeine |
|---|---|
| Brewed coffee (8 oz / 240 ml) | ~95 mg |
| Espresso shot | ~63 mg |
| Black tea (8 oz / 240 ml) | ~47 mg |
| Green tea (8 oz / 240 ml) | ~28 mg |
| Energy drink (8.4 oz / 250 ml) | ~80 mg |
| Cola (12 oz / 355 ml) | ~34 mg |
Want everyday habits to try alongside this estimate? Read our practical guide to better sleep.
Frequently asked questions
What is caffeine half-life?
The time it takes your body to clear half of the caffeine. It averages about 5 hours in healthy adults but ranges from about 3 to 7 hours depending on genetics, medication, pregnancy, smoking, and liver function.
How much caffeine is too close to bedtime?
There is no established safe amount. A well-known study found that 400 mg taken 6 hours before bed still reduced sleep. The bedtime target in this tool (10, 25 or 50 mg) is a number you choose for the calculation; it is not a proven no-effect dose.
Are the drink amounts exact?
No. Caffeine content varies by brand, roast, and brewing. Use the custom field if you know your exact dose.
Is this medical advice?
No. It is a simple decay estimate. Talk to a clinician if you have heart, anxiety, or pregnancy-related concerns about caffeine.
