At One Place

If I go to bed at 9:15 pm, what time should I wake up?

Going to bed at 9:15 pm
Wake between 4:30 am and 6:30 am
Asleep around 9:30 pm, allowing 15 minutes to drop off

If you are in bed at 9:15 pm and asleep by about 9:30 pm, seven hours takes you to 4:30 am and nine hours to 6:30 am. Seven is the floor the American Academy of Sleep Medicine sets for adults; the upper end is where most people stop gaining.

When your alarm should go

All of these allow 15 minutes to fall asleep, which is the middle of the normal range. Consistently taking under five minutes usually means you are short on sleep; consistently taking more than half an hour is the definition used for sleep-onset insomnia.
Sleep Wake at Cycles at 90 minutes
6 hours 3:30 am Exactly 4
6.5 hours 4:00 am 4.3 — mid-cycle
7 hours 4:30 am 4.7 — mid-cycle
7.5 hours 5:00 am Exactly 5
8 hours 5:30 am 5.3 — mid-cycle
8.5 hours 6:00 am 5.7 — mid-cycle
9 hours 6:30 am Exactly 6

Cycle-aligned wake times

Cycles Time asleep Wake at
4 cycles 6 hours 3:30 am
5 cycles 7 hours 30 minutes 5:00 am
6 cycles 9 hours 6:30 am

The cycle-aligned times below assume a flat 90-minute cycle, which is a population average rather than a fact about any one night. Real cycles run about 70 to 120 minutes, the first ones are shorter than the later ones, and their composition shifts from deep sleep towards REM as the night goes on. Treat the numbers as a target to aim at, not a schedule to hit. Total sleep matters considerably more than which minute you wake on.

Working backwards from this bedtime

Last coffee
1:15 pm — eight hours before bed, so roughly a quarter of the caffeine is left
Last large meal
6:15 pm, to let digestion settle
Alcohol
Shortens sleep onset and then fragments the second half of the night, so it costs more sleep than it buys
Screens
Bright light suppresses melatonin; dimming from about 8:15 pm is the usual advice

How much sleep you need

Age Per day Notes
Babies, 4 to 12 months 12 to 16 hours, including naps Counting naps. Sleep at this age is still spread across the day and the total is what matters, not the shape of it.
Toddlers, 1 to 2 years 11 to 14 hours, including naps Counting naps. Most children drop to a single daytime nap somewhere in this band.
Preschoolers, 3 to 5 years 10 to 13 hours, including naps Counting naps, which most children stop taking towards the end of this band.
Children, 6 to 12 years 9 to 12 hours Naps have usually stopped by now, so this is night sleep.
Teenagers, 13 to 18 years 8 to 10 hours Adolescent circadian timing shifts later by one to three hours at puberty, which is a biological change and not a behavioural one. A teenager who cannot fall asleep at 10 pm is usually not being difficult, and an early school start subtracts from the wrong end of the night.
Adults, 18 and over 7 or more hours The consensus statement gives a floor, not a range: seven or more hours on a regular basis. It does not endorse eight as a target, and it declines to state an upper bound, because regularly sleeping more than nine hours is associated with poor health outcomes without the direction of causation being established.

Common questions

If I go to bed at 9:15 pm, when should I wake up?
Between 4:30 am and 6:30 am, assuming you are asleep about 15 minutes after getting in.
How much sleep is that if I wake at 5:30 am?
Eight hours of sleep, and eight hours 15 minutes in bed.
When should I have stopped drinking coffee?
Caffeine has a half-life of roughly five hours, so a cup at 4:15 pm still has half its caffeine in you at 9:15 pm. Eight hours before bed — 1:15 pm — leaves about a quarter.

Related pages

Sources

  1. Recommended Amount of Sleep for a Healthy Adult: A Joint Consensus Statement — Watson et al., Sleep 38(6) / Journal of Clinical Sleep Medicine, 2015
  2. Normal Human Sleep: An Overview — Carskadon & Dement, Principles and Practice of Sleep Medicine, 6th ed., 2017
  3. US Food and Drug Administration — FDA (Public domain (US Government))

How these figures are compiled and checked