Sleep Cycle Calculator

Light Sleep (NREM 1 and 2) — about 45 minutes

Your body relaxes, heart rate slows, and your brain begins filtering the day. This is the stage you cycle through most often. Waking during light sleep is why you feel refreshed when your alarm hits at the right time.

Deep Sleep (NREM 3) — about 20 minutes

Your body does most of its physical repair here. Immune function, muscle recovery, and cell growth all happen during deep sleep. You get more deep sleep in the first half of the night, which is why the first two or three cycles matter most for feeling physically rested.

REM Sleep — about 20 minutes, longer in later cycles

REM is where memory consolidation, emotional processing, and dreaming happen. Your REM cycles get significantly longer as the night goes on, which means cutting your sleep short by one cycle often means losing your most mentally restorative period of the night.