If I go to bed at 8:30 PM, what time should I wake up?
Falling asleep around 8:45 PM, the best wake-up times are 4:15 AM (5 cycles) or 5:45 AM (6 cycles), so your alarm lands at the end of a 90-minute cycle.
Best wake-up times after a 8:30 PM bedtime
| Wake up at | Cycles | Total sleep |
|---|---|---|
| 5:45 AM — best | 6 | 9 hours |
| 4:15 AM | 5 | 7.5 hours |
| 2:45 AM | 4 | 6 hours |
These assume about 15 minutes to fall asleep, so you are actually asleep by 8:45 PM. A 4:15 AM alarm completes 5 full cycles for a standard work morning; 5:45 AM completes all 6 for the fullest night.
How long is sleep from 8:30 PM?
From a 8:30 PM bedtime, five 90-minute cycles plus the time to fall asleep brings you to 4:15 AM (about 7.5 hours of sleep), and six cycles to 5:45 AM (about 9 hours). Four cycles gives a shorter 2:45 AM wake-up (~6 hours) if you have to be up early. Waking on the border between cycles, rather than midway through deep sleep, is what spares you the heavy-headed start.
Making 8:30 PM work as a bedtime
To make 8:30 PM stick, give yourself a screen-free, dimly lit hour before bed, cool the room down, and hold the same wake-up time every day so your body clock settles. If your morning alarm is the fixed point rather than the bedtime, start from the relevant wake-up page and work backwards to the bedtime that fits.
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