Sleep Calculator: When to Go to Bed or Wake Up

Type the time you need to get up, or the time you are going to bed, and get six bedtimes or wake-up times that line up with the end of a 90-minute sleep cycle.

Runs in your browserFree, no sign-upLast reviewed October 13, 2026

Bedtimes for waking at 7:00 AM

6 cycles (9 hr asleep): 9:45 PM; 21:45, night before
5 cycles (7 hr 30 min asleep): 11:15 PM; 23:15, night before
4 cycles (6 hr asleep): 12:45 AM; 00:45, same day
Asleep by (5 cycles): 11:30 PM; 15 minutes after getting into bed

All bedtime options

Sleep cycles	Time asleep	Go to bed at	24-hour	Day	Time in bed	7 or more hours asleep
6	9 hr	9:45 PM	21:45	Night before	9 hr 15 min	Yes
5	7 hr 30 min	11:15 PM	23:15	Night before	7 hr 45 min	Yes
4	6 hr	12:45 AM	00:45	Same day	6 hr 15 min	No
3	4 hr 30 min	2:15 AM	02:15	Same day	4 hr 45 min	No
2	3 hr	3:45 AM	03:45	Same day	3 hr 15 min	No
1	1 hr 30 min	5:15 AM	05:15	Same day	1 hr 45 min	No

Summary

To wake up at 7:00 AM (07:00) at the end of a 90-minute sleep cycle, allowing 15 minutes to fall asleep, go to bed at 9:45 PM for 9 hours of sleep, 11:15 PM for 7.5 hours or 12:45 AM for 6 hours.

An estimate, not medical advice. These times assume every sleep cycle lasts exactly 90 minutes. Real cycles vary from person to person and through the night, so treat the results as a starting point. Health bodies advise 7 or more hours of sleep a night for most adults. Speak to a doctor about ongoing sleep problems.

Quick answers

What time should I go to bed to wake up at 6 AM?: Go to bed at 10:15 PM for 7.5 hours of sleep (five 90-minute cycles) or 8:45 PM for 9 hours (six cycles), allowing 15 minutes to fall asleep. 11:45 PM gives four cycles, which is 6 hours and below the 7 or more hours advised for adults.
What time should I go to bed to wake up at 7 AM?: With 15 minutes to fall asleep, 11:15 PM gives five full cycles (7.5 hours asleep) and 9:45 PM gives six (9 hours). The next option, 12:45 AM, gives four cycles and 6 hours of sleep.
If I go to bed at 10 PM, what time should I wake up?: Taking 15 minutes to fall asleep, 90-minute cycles end at 5:45 AM after 7.5 hours of sleep and 7:15 AM after 9 hours. The earlier cycle end, 4:15 AM, comes after only 6 hours.
How long is a sleep cycle?: About 90 minutes on average in adults, though individual cycles commonly run anywhere from roughly 70 to 120 minutes. Each cycle moves through light sleep, deep sleep and REM sleep. Earlier cycles in the night tend to be shorter than later ones.
How many sleep cycles do I need a night?: Five or six 90-minute cycles give 7.5 or 9 hours, which fits the general advice of 7 or more hours a night for adults. Four cycles is 6 hours, less than that advice. Individual needs vary.
Is it better to wake up at the end of a sleep cycle?: Many people find it easier to get up from light sleep than from deep sleep, and grogginess on waking, called sleep inertia, tends to be worse after waking from deep sleep. A calculator can only estimate where a cycle ends, so treat the times as a guide.

Why use Sleep Calculator

Enter a wake-up time and this sleep calculator counts back in 90-minute cycles, then takes off the minutes you need to fall asleep, to give six bedtimes covering 1.5 to 9 hours of sleep. Switch the first field and it works forward from a bedtime to six wake-up times instead. To wake at 7:00 AM with the default 15 minutes to fall asleep, go to bed at 11:15 PM for five cycles (7.5 hours asleep) or 9:45 PM for six cycles (9 hours). The results are estimates: 90 minutes is an average cycle length, and real cycles differ between people and across a single night.

What time to go to bed for each wake-up time

Bedtimes for 6, 5 and 4 sleep cycles of 90 minutes, with 15 minutes allowed to fall asleep. Times after midnight are on the same day as the alarm.

Wake-up time	Bed for 9 hours (6 cycles)	Bed for 7.5 hours (5 cycles)	Bed for 6 hours (4 cycles)
5:00 AM	7:45 PM	9:15 PM	10:45 PM
6:00 AM	8:45 PM	10:15 PM	11:45 PM
6:30 AM	9:15 PM	10:45 PM	12:15 AM
7:00 AM	9:45 PM	11:15 PM	12:45 AM
7:30 AM	10:15 PM	11:45 PM	1:15 AM
8:00 AM	10:45 PM	12:15 AM	1:45 AM

If you fall asleep faster or slower than 15 minutes, move every bedtime later or earlier by the difference, or change Time to fall asleep in the calculator.

What time to wake up for each bedtime

Wake-up times at the end of 4, 5 and 6 cycles, again with 15 minutes to fall asleep after getting into bed.

Bedtime	After 6 hours (4 cycles)	After 7.5 hours (5 cycles)	After 9 hours (6 cycles)
9:30 PM	3:45 AM	5:15 AM	6:45 AM
10:00 PM	4:15 AM	5:45 AM	7:15 AM
10:30 PM	4:45 AM	6:15 AM	7:45 AM
11:00 PM	5:15 AM	6:45 AM	8:15 AM
12:00 AM	6:15 AM	7:45 AM	9:15 AM

How bedtime is worked out from 90-minute cycles

Bedtime = wake-up time - (cycles x 90 minutes) - minutes to fall asleep. Wake-up time = bedtime + minutes to fall asleep + (cycles x 90 minutes).

For a 7:00 AM alarm and five cycles: 5 x 90 = 450 minutes, or 7 hours 30 minutes, which puts the start of sleep at 11:30 PM. Taking off 15 minutes to fall asleep gives a bedtime of 11:15 PM and 7 hours 45 minutes in bed. The calculator repeats this for 6, 5, 4, 3, 2 and 1 cycles, wraps the clock around midnight and labels each result as the night before, the same day or the next day. The Time in bed column is sleep time plus the minutes to fall asleep, and the last column says whether the sleep time reaches 7 hours.

Worked examples with different fall-asleep times

Planning from the moment you fall asleep

When to wake up; time 23:45; Time to fall asleep 0

Wake at 5:45 AM (4 cycles, 6 hr), 7:15 AM (5 cycles, 7 hr 30 min) or 8:45 AM (6 cycles, 9 hr), all on the next day.

Midnight bedtime, slower to drop off

When to wake up; time 12am; Time to fall asleep 20

Asleep by 12:20 AM. Wake at 6:20 AM, 7:50 AM or 9:20 AM for 4, 5 or 6 cycles.

Night shift worker getting up at noon

When to go to bed; time 12:00 pm; Time to fall asleep 30

Go to bed at 2:30 AM for 9 hours of sleep, 4:00 AM for 7.5 hours or 5:30 AM for 6 hours, all on the same day as the alarm.

Early start

When to go to bed; time 5:00; Time to fall asleep 15

Go to bed at 7:45 PM (6 cycles), 9:15 PM (5 cycles) or 10:45 PM (4 cycles) the night before.

Recommended hours of sleep by age

General public health guidance on sleep in each 24 hours, as published by the US Centers for Disease Control and Prevention from American Academy of Sleep Medicine and Sleep Research Society recommendations.

Age group	Recommended sleep	Closest number of 90-minute cycles
School age, 6 to 12 years	9 to 12 hours	6 to 8
Teen, 13 to 17 years	8 to 10 hours	6
Adult, 18 to 60 years	7 or more hours	5 or 6
Adult, 61 to 64 years	7 to 9 hours	5 or 6
Adult, 65 years and older	7 to 8 hours	5

The calculator lists up to 6 cycles (9 hours). Children under 6 need more sleep, including naps, and their cycles are shorter than 90 minutes, so this tool is not suited to them.

What this estimate can and cannot tell you

The arithmetic is exact; the assumption behind it is not. Ninety minutes is an average. Cycle length differs from person to person and from one cycle to the next, and brief awakenings shift the pattern. By the fifth or sixth cycle a small difference in cycle length adds up to a large one, so a calculated time may not land on light sleep for you.

The time to fall asleep is also a guess. Most healthy adults drop off within about 10 to 20 minutes, but caffeine, stress, naps and screen use can stretch that.

Use the times as a starting point. If a suggested bedtime leaves you groggy, move it 15 minutes earlier or later for a few nights and compare. Total sleep and a regular schedule matter more than hitting an exact minute. This page gives general information, not medical advice: if you regularly struggle to fall asleep, stay asleep or stay awake during the day, talk to a doctor.

How to get your result

1
In I want to know, choose When to go to bed if you have a fixed wake-up time, or When to wake up if you know your bedtime.
2
Type the time in Wake-up time or bedtime, as 24-hour (06:30) or 12-hour with am or pm (6:30 am).
3
Set Time to fall asleep in minutes. It starts at 15; use 0 to count from the moment you fall asleep.
4
Read the three highlighted times for 6, 5 and 4 cycles, then the full table for every option from 6 cycles down to 1.
5
Check the Day column to see whether a time falls the night before, the same day or the next day, and copy the Summary if you want to save it.

Questions people ask

Does this tool know what time it is now?

No. It never reads your device clock. To answer the question of when to wake up if you go to sleep now, choose When to wake up and type the current time as the bedtime.

Why is the default time to fall asleep 15 minutes?

It sits in the middle of the 10 to 20 minutes that is typical for healthy adults. If you usually lie awake longer, raise it. The field accepts whole minutes from 0 to 120.

Can I change the cycle length from 90 minutes?

No. Every cycle is fixed at 90 minutes. If you know your cycles run longer or shorter, for example from a sleep tracker, you can approximate it by adjusting the time to fall asleep, but the results will be rougher.

Is 6 hours of sleep enough?

For most adults it is less than recommended. General guidance is 7 or more hours a night for adults aged 18 to 60. The table marks four cycles and fewer as No in the 7 or more hours column for that reason.

What time formats can I type?

24-hour times such as 07:00, 7:00, 0730 or 22.30, and 12-hour times such as 7am, 7:30 am or 10:45 p.m. Noon is 12 pm and midnight is 12 am or 00:00. Anything else returns a message asking for a valid time.

Does the Time in bed column include falling asleep?

Yes. Time asleep is the cycles alone, and Time in bed adds the minutes to fall asleep. Five cycles with 15 minutes to fall asleep is 7 hr 30 min asleep and 7 hr 45 min in bed.

Can I use it to time a nap?

You can read the 1-cycle row, which gives a 90-minute sleep plus your time to fall asleep. Going to bed at 10:00 PM with 15 minutes to fall asleep, one cycle ends at 11:45 PM. The tool has no option for short naps of 10 to 30 minutes.