Sleep Calculator
Find the best time to go to bed or wake up based on 90-minute sleep cycles. Waking between cycles helps you feel more alert and refreshed.
Go to bed at
11:15 pm
Wake-up time
7:00 am
Best bedtime (5 cycles)
11:15 pm
7h 30m of sleep
Suggested bedtimes
9:45 pm
6 cycles · 9h
11:15 pm
5 cycles · 7h 30m
12:45 am
4 cycles · 6h
Why sleep cycles matter: Sleep occurs in ~90-minute cycles, each progressing through light sleep, deep sleep, and REM. Waking at the end of a cycle (rather than mid-cycle) helps you feel more alert and refreshed (Carskadon & Dement, 2005, Principles and Practice of Sleep Medicine).
NHS recommendation: Most adults need 7 to 9 hours of sleep per night. That's 5 to 6 complete 90-minute cycles. Consistently getting less than 6 hours is associated with increased risk of cardiovascular disease, obesity, and impaired cognitive function (Walker, 2017).
Sleep onset latency: The average healthy adult takes 10-20 minutes to fall asleep (Ohayon et al., 2004, Sleep Medicine Reviews). If you regularly fall asleep in under 5 minutes, it may indicate sleep deprivation. If it takes over 30 minutes, consider sleep hygiene improvements.