Caffeine cutoff calculator.
Caffeine has a 5-hour half-life — that 4 PM coffee is still 25% active at midnight. Here's your real cutoff time.
Quick fill
Cutoff time
No caffeine after 6:22 PM
Cut off caffeine 4.6 hours before bed
Calculated using a 5-hour caffeine half-life and a 50mg sleep-disruption threshold. Half-life varies by genetics — slow CYP1A2 metabolizers should add 1–3 hours to the cutoff.
Why this matters.
Caffeine works by blocking adenosine receptors — the molecule that makes you feel sleepy. Even when you fall asleep with caffeine still in your system, it suppresses deep (slow-wave) sleep by up to 20%. You can sleep 8 hours and still feel like you slept 6.
The 5-hour figure is an average for healthy adults. People with the slow variant of the CYP1A2 enzyme can have half-lives closer to 8 hours. If coffee at noon still keeps you up, you're probably one of them.