What time should I go to bed if I wake up at 8:45 am?

A 8:45 am alarm is the most common one people ask about, and the answer is 1:00 am for five cycles or 11:30 pm for six.

Why three times and not one

The middle option, 1:00 am, is five cycles and 7 h 30 min of actual sleep; 11:30 pm is six cycles and 9 h. Both sit inside the adult range. The 2:30 am option is 6 h: enough to get through the day, not enough to do it twice.

Sleep moves from light sleep into deep sleep and then REM, and one pass takes about 90 minutes — anywhere from 70 to 120 depending on the person and the point in the night. That spread is why these are windows, not appointments.

Walk through the night from a 1:00 am lights-out: asleep by about 1:15 am, into the first stretch of deep sleep around 1:35 am, first REM period near 2:30 am, the halfway point of the night at 5:00 am, and the longest REM period of the night starting around 8:10 am — which is what a 8:45 am alarm at the end of cycle 5 lets you finish.

All bedtimes for a 8:45 am 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 1:00 am

If 1:00 am comes and your mind is still running, aim for the next cycle boundary at 2:30 am instead of counting the minutes. Ten to twenty minutes to fall asleep is normal; much longer, repeatedly, is worth a conversation with a clinician rather than a calculator.

Try a different time