What time should I go to bed if I wake up at 12:45 pm?

Waking at 12:45 pm is a shift-worker's morning. Five cycles start at 5:00 am, six at 3:30 am — both in daylight, which makes blackout curtains the real bedtime tool.

Why three times and not one

The middle option, 5:00 am, is five cycles and 7 h 30 min of actual sleep; 3:30 am is six cycles and 9 h. Both sit inside the adult range. The 6:30 am option is 6 h: enough to get through the day, not enough to do it twice.

Each cycle runs light sleep, deep sleep, then REM. Ninety minutes is the average; the real figure drifts between 70 and 120 minutes, and the first cycle of the night is usually the shortest.

Walk through the night from a 5:00 am lights-out: asleep by about 5:15 am, into the first stretch of deep sleep around 5:35 am, first REM period near 6:30 am, the halfway point of the night at 9:00 am, and the longest REM period of the night starting around 12:10 pm — which is what a 12:45 pm alarm at the end of cycle 5 lets you finish.

All bedtimes for a 12:45 pm alarm

Formula: bedtime = wake time − (cycles × 90 min) − 15 min · adult range from the NSF 2015 panel and the AASM/SRS 2015 consensus · methodology

If you can't fall asleep by 5:00 am

Two things stretch the fifteen minutes most people need to drop off: caffeine within six hours of 5:00 am (that is 11:00 pm), and a screen in the last hour. If neither applies and you are still awake twenty minutes in, get up for a while rather than lying there, and come back for the 6:30 am window.

Try a different time