Bedtime calculator

Pick your wake time and how much sleep you need. Get a bedtime, a wind-down time and a caffeine cutoff.

Works offline. Nothing you enter leaves your browser.

How it works

It counts back from your wake time:

• Lights out = wake time − the sleep you need − the time you usually take to fall asleep.
• Wind-down starts 30 to 60 minutes before that.
• Last caffeine is 9 hours before lights out. A 2023 meta-analysis found that a regular coffee needs at least 8.8 hours to clear enough to avoid losing sleep [5].

How much sleep you need: adults should get 7 hours or more on a regular basis [1]. If you wake up before your alarm and feel fine all day, you may need less than you’ve set. If you’re sleepy every afternoon, try 30 minutes more for a week.

Time to fall asleep: 30 minutes or less is one of the markers of good sleep [4]. Use your usual time, not your best night.

Why it doesn’t use 90-minute cycles

Many bedtime calculators count back in 90-minute “cycles” so you wake at the end of one. We don’t, because cycles aren’t that regular:

• In 369 healthy people recorded in a sleep lab, the median cycle was 96 minutes, with large differences between people. The first cycle of the night was consistently shorter than the rest [2].
• Differences between people were much bigger than differences between one night and the next [3].
• The time you take to fall asleep changes from night to night too.

So a calculator can’t know when your cycles end, and after a few hours the error adds up to more than a whole cycle. A fixed wake time and enough total sleep matter more than waking at the “right” moment.

Using the result: consistent wake time, wind-down routine, sleep stages and cycles.