What time should I go to bed if I wake up at 7:00 pm?

Waking at 7:00 pm is a night-shift schedule: sleep runs through the day, with lights out at 11:15 am for five cycles or 9:45 am for six.

Why three times and not one

The middle option, 11:15 am, is five cycles and 7 h 30 min of actual sleep; 9:45 am is six cycles and 9 h. Both sit inside the adult range. The 12:45 pm 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 11:15 am is a target and not a deadline.

Here is the shape of the night. You settle at 11:15 am and are asleep by 11:30 am; the first and deepest slow-wave stretch arrives near 11:50 am; by 3:15 pm you are halfway through; from about 6:25 pm the final REM period runs up to the 7:00 pm alarm. Cut the night short and that last REM block is what goes.

All bedtimes for a 7:00 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

7:00 pm: for parents on nights and for 11 pm starts

A 7:00 pm alarm is what a night-working parent often ends up with: home at 7:30 am, school run, back by 9, asleep at 9:45 am for six cycles or 11:15 am for five. Both end at 7:00 pm, in time for a family dinner before a 10 or 11 pm start. The four-cycle bedtime is 12:45 pm, after lunch, and it is a better fallback than it looks: early afternoon is when alertness dips for nearly everyone, so falling asleep then is easier than at 9 am.

Check the gap to your shift. Before an 11 pm start you have four hours, which is comfortable. Before a 7 pm start you have none, so this alarm is wrong for twelve-hour nights; the 4:00 pm alarm is the one that fits those. Bedtimes this late push the caffeine line late as well: 5:15 am for a 11:15 am bedtime, which means coffee during the shift is fine and the one with breakfast afterwards is not. At 7 am you will have been awake 12 hours. If you wake by yourself at 5 or 6 pm and cannot drop off again, get up; lying there until 7:00 pm does not add sleep, and the extra evening is worth more than the extra hour in bed.

Every alarm in the 7 pm hour

Lights-out times for each alarm · last coffee = six hours before the five-cycle bedtime (Drake 2013) · full grid on the open data page

If you can't fall asleep by 11:15 am

If 11:15 am comes and your mind is still running, aim for the next cycle boundary at 12:45 pm 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