Caffeine calculator
Caffeine has a half-life of about 5–6 hours, which means half of it is still in your bloodstream long after your last cup. Enter your bedtime to get a recommended caffeine cut-off — or check how much caffeine from a specific drink is left when your head hits the pillow.
Check a specific drink
Want to know how much of a particular coffee is still active at bedtime? Enter when you drank it and how much caffeine it contained.
Why caffeine timing matters
Caffeine works by blocking adenosine, the molecule that builds up through the day to make you feel sleepy. So caffeine doesn’t add energy — it masks your sleep pressure. Even when you manage to fall asleep with caffeine in your system, studies show it reduces deep sleep and overall sleep quality, so you wake less rested without knowing why.
Because the half-life is roughly 5–6 hours, a strong coffee at 4 PM can still have a meaningful dose circulating at midnight. As a rule of thumb, stopping caffeine at least 6 hours before bed lets most of it clear. Sensitivity varies a lot with genetics, age, and tolerance, so if you’re a slow metaboliser you may need an even earlier cut-off.
Put it together
Once you’ve protected your evening from caffeine, time your bedtime so you wake at the end of a sleep cycle. Use the sleep cycle calculator to find the right bedtime, and our guide to falling asleep faster for more evening habits that work.