Caffeine should be sleep-friendly by
You took in — of caffeine. It has a half-life of about 5.5 hours.
| Time after your drink | Caffeine left |
|---|
How long does caffeine stay in your system?
Caffeine has a half-life of roughly 5 to 6 hours, which means about half of it is still in your body five to six hours after your last sip — and a quarter is there ten to twelve hours later. That afternoon coffee can quietly sabotage your sleep long after you’ve forgotten about it. This calculator estimates how much caffeine is left over time and when it drops to a sleep-friendly level, so you know your personal “caffeine curfew”.
Estimates use an average half-life of 5.5 hours. Your real rate varies with genetics, pregnancy, medications and smoking — treat this as a helpful guide, not a medical measurement.
Frequently Asked Questions
How many hours before bed should I stop caffeine?
A common guideline is to avoid caffeine for at least 6–8 hours before bed, and sensitive people even longer. This calculator gives you a specific “sleep-friendly” time based on your drink and sensitivity.
Does caffeine really affect sleep that much?
Yes — even when you fall asleep fine, caffeine can reduce deep sleep and leave you less rested. Studies show caffeine taken 6 hours before bed can still cut into sleep.
Why does the “safe” time depend on my sensitivity?
People clear caffeine at different rates and feel it differently. The calculator lowers the target level for sensitive sleepers, so it suggests an earlier caffeine curfew for them.
Is decaf caffeine-free?
Not entirely — decaf coffee still has a small amount (around 2–5 mg per cup), which is low enough that it rarely affects sleep.