Why it matters
Caffeine stays longer than you think.
Caffeine's half-life is roughly 5-6 hours. A 200 mg coffee at 2 pm still leaves about 100 mg in your system near 7:30 pm and about 50 mg near midnight — enough to delay and lighten sleep. The tools here make that timing visible, so you can act on it tonight.
All tools are free, plain-text, and open instantly. No account, no download.
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.