Free calculator
What time should I go to bed?
Four bedtime options, built from your wake time — not from willpower.
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Sleep
How the bedtimes are calculated
Sleep cycles last about 90 minutes. The calculator subtracts four, five or six cycles plus the time you usually take to fall asleep from your wake-up time, and shows the corresponding bedtimes.
Why the number of cycles matters
Waking in the middle of deep sleep feels worse than waking after a complete cycle, even after the same total hours. Five cycles suits many adults; the right number is the one that leaves you alert, not the one on a poster.
Who it is for
Shift workers, early starters and anyone experimenting with a consistent bedtime.
Frequently asked questions
Is 90 minutes exact?
No. Cycles vary between roughly 70 and 120 minutes and change through the night. Treat the output as a planning aid and adjust the cycle length if your own pattern differs.
Does falling asleep faster change the result?
Yes. The fall-asleep buffer is added before the cycles, so a shorter buffer moves every bedtime later.
Should I use this every night?
A consistent wake time is more useful than chasing perfect cycle alignment. Use the calculator to set a realistic bedtime, then keep it.