Log in Sign up free

Sleep Calculator

Find the best time to go to bed or wake up, based on 90-minute sleep cycles.

Runs instantly in your browser — results update as you type.

What time should I go to sleep to wake up at 6:30?

Count back in 90-minute sleep cycles from your wake-up time, plus about 15 minutes to fall asleep. To wake at 06:30 after 6 cycles (9 hours) go to bed at 21:15; after 5 cycles (7.5 hours) at 22:45.

How much sleep?

  • Adults: 7–9 hours (5–6 cycles).
  • Teenagers: 8–10 hours.
  • Waking at the end of a cycle, in light sleep, reduces grogginess.

Frequently asked questions

Are sleep cycles always 90 minutes?

They range from about 80 to 110 minutes; 90 is a good average.

What if I take longer to fall asleep?

Change the “minutes to fall asleep” value.

Is it free?

Yes.