Free health tool

Sleep Calculator

To wake at 7:00 after five full sleep cycles (7.5 hours), aim to be in bed around 23:15. Most adults need 7 or more hours of sleep a night.

Pick a time to see suggested bedtimes or wake-up times.

Calculated in your browser. Nothing you enter is sent or stored.

How this tool works

1Choose whether you know your wake-up time or your bedtime.
2The tool assumes about 15 minutes to fall asleep and sleep cycles of about 90 minutes.
3It suggests times that complete 4, 5 or 6 cycles (6, 7.5 or 9 hours of sleep).

Formula: Bedtime = wake-up time − (cycles × 90 min) − 15 min

Real sleep cycles vary from roughly 70 to 120 minutes and change through the night, so treat the times as a guide.
Getting enough total sleep regularly matters more than hitting an exact cycle.
If you often feel unrefreshed, snore loudly or stop breathing in your sleep, talk to a doctor.