How it works
Caffeine is processed by the liver and its half-life is about 5-6 hours for most adults. This calculator uses that rule to show when your caffeine drops to each level — 50%, 25%, and roughly 10%.
The important number is the last one: the latest time you can drink coffee before a 23:00 bedtime. For most people that is around mid-afternoon. Change your bedtime and the number updates.
Use the inputs to match your own body. If you are very sensitive, treat the earlier suggestion as your cutoff. If you rarely feel caffeine, you may be fine slightly later — but most people underestimate how much late caffeine affects them.
Pair this with the intake calculator to see your full day, and the taper plan if you want to reduce.
Questions people actually ask
How long does caffeine stay in your system?
For most adults it takes 5-6 hours to drop to half, and 10-12 hours to be mostly gone. An afternoon coffee can still be affecting you past midnight.
What is the half-life of caffeine?
The half-life is the time for half the caffeine to be removed, usually 5-6 hours for a healthy adult. It varies with genetics, weight, and some medications.
What time should I stop drinking coffee?
A common rule is to stop about 8-10 hours before bed. If you sleep at 23:00, that usually means no coffee after 13:00-15:00.
Does the calculator give exact times?
No, it gives an estimate based on a typical half-life. Your body may clear caffeine faster or slower.
Why does caffeine affect me more than my friend?
Weight, genetics, regular use, and medications all change how fast you clear caffeine. Two people can react very differently to the same cup.
Does decaf count toward my caffeine?
Decaf has a small amount, usually 2-15 mg per cup, which matters little for most people but can add up for sensitive sleepers.