Find the best time to go to bed or wake up, based on complete 90-minute sleep cycles and a 14-minute average time to fall asleep — plotted on a 24-hour clock so you can see it at a glance.
A full sleep cycle lasts about 90 minutes and moves through light sleep, deep sleep, and REM sleep. Most adults need 5 to 6 complete cycles per night — roughly 7.5 to 9 hours. This calculator adds about 14 minutes for the average time it takes to fall asleep, then counts backward or forward in 90-minute blocks from your target time.
Waking up at the boundary between cycles, rather than in the middle of deep sleep, is generally associated with feeling more refreshed — which is why the calculator gives you several options instead of a single number, with 5 and 6 cycles marked as recommended.
It uses average sleep cycle length (about 90 minutes) to suggest times aligning with completing full cycles.
Waking during deep sleep phases tends to cause grogginess, known as sleep inertia.
About 5-6 complete 90-minute cycles, roughly 7.5-9 hours total.