Sleep Calculator — Best Bedtimes & Wake Times by Sleep Cycle

Sleep is structured around repeating 90-minute cycles, each passing through light sleep, deep slow-wave sleep, and REM. Most adults need five or six of these cycles — roughly 7.5 to 9 hours — to feel fully rested. The key to waking refreshed is finishing a complete cycle just before your alarm goes off, so you surface during the lightest sleep stage rather than being jolted out of deep sleep mid-cycle.

The calculator accounts for the 14-minute average it takes a healthy adult to fall asleep (sleep-onset latency). In Wake mode it counts backward: from your alarm time, subtract 14 minutes, then subtract full 90-minute blocks to find the bedtimes that keep you in a natural cycle. In Bed mode it counts forward from your intended sleep time, adding the same 14-minute onset before counting cycles. Power Nap mode simply adds your chosen nap length to the start time so you can set a precise alarm — 20 minutes ends before slow-wave sleep begins, while 90 minutes completes a full cycle.

The 90-minute figure is a research average, not a universal constant. Individual cycles range from roughly 70 to 120 minutes and tend to lengthen across the night as REM periods extend. If the suggested times don’t feel right after a few nights, shift them by 10–15 minutes in either direction to calibrate to your own rhythm. The calculator gives you a science-based starting point; listening to how you feel provides the final adjustment.