What time should I go to bed if I wake up at 8:30 am?

A 8:30 am alarm is the most common one people ask about, and the answer is 12:45 am for five cycles or 11:15 pm for six.

Why three times and not one

The middle option, 12:45 am, is five cycles and 7 h 30 min of actual sleep; 11:15 pm is six cycles and 9 h. Both sit inside the adult range. The 2:15 am option is 6 h: enough to get through the day, not enough to do it twice.

The three times are ninety minutes apart because that is the average length of one trip through light, deep and REM sleep. Real cycles vary — 70 to 120 minutes, shorter early in the night — which is why 12:45 am is a target and not a deadline.

Walk through the night from a 12:45 am lights-out: asleep by about 1:00 am, into the first stretch of deep sleep around 1:20 am, first REM period near 2:15 am, the halfway point of the night at 4:45 am, and the longest REM period of the night starting around 7:55 am — which is what a 8:30 am alarm at the end of cycle 5 lets you finish.

All bedtimes for a 8:30 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 12:45 am

The fifteen minutes built into each time is the average sleep-onset latency for healthy adults. Past twenty minutes of lying awake after 12:45 am, the standard advice is to get out of bed until you feel sleepy rather than trying harder. Steady sound helps some people here: one small lab study found broadband noise cut the time to fall asleep by about 38%, though a 2021 review rated the evidence overall as low quality.

Try a different time