Caffeine Half-Life Calculator
How much caffeine will still be in your system when you try to sleep?
How this works
What's the half-life of caffeine?
About 5 hours for most adults. That means 5 hours after you drink it, you still have half. Ten hours after, a quarter. It's not gone for 20+ hours.
When should I stop drinking caffeine before bed?
If you want minimal sleep impact, eight hours before bed. So a 10 PM bedtime means last caffeine by 2 PM. If you have ~6 hours of buffer you're usually fine; less than that and you'll likely feel it.
Does decaf still have caffeine?
Yes. An 8 oz cup of decaf still has 2-15 mg. Not enough to wreck anyone's sleep, but if you're already sensitive and drinking it after dinner it can add up.
This is a rough estimate. Real metabolism varies wildly by genetics, liver function, and other meds. Use it as a guide, not a prescription.