acalculator

When should I go to sleep?

Enter the time you need to wake up, or the time you go to bed. See bedtimes or wake-up times that fit whole 90-minute sleep cycles.

Your numbers

I know my
More options
Go to bed at
11:15 PM

To wake up at 7:00 AM after 5 full sleep cycles, go to bed at 11:15 PM.

Or, for 6 cycles (9 h of sleep)
9:45 PM
Or, for 4 cycles (6 h of sleep)
12:45 AM
In short
To wake up at 7:00 AM after 5 full sleep cycles, go to bed at 11:15 PM.

Go to bed at: 11:15 PM. To wake up at 7:00 AM after 5 full sleep cycles, go to bed at 11:15 PM.

This calculator gives general information only. It is not medical advice and does not replace a doctor or other health care provider. Talk with a professional about your results. Terms of use

How to calculate

Finds bedtimes that let you wake up at the end of a 90-minute sleep cycle, or wake-up times for a given bedtime, allowing for the minutes it takes to fall asleep.

Example with the default inputs (I know my Wake-up time, Wake up at 07:00, Minutes to fall asleep 15): To wake up at 7:00 AM after 5 full sleep cycles, go to bed at 11:15 PM.

Method: Bedtime = wake-up time − minutes to fall asleep − cycles × 90 minutes; wake-up time = bedtime + minutes to fall asleep + cycles × 90 minutes; times wrap past midnight.

  • A sleep cycle lasts 90 minutes. Real cycles run about 90 to 110 minutes and vary through the night.
  • Waking at the end of a cycle, not in the middle of deep sleep, is assumed to feel easier.
  • Adults need 7 hours of sleep or more (AASM and Sleep Research Society), so 5 or 6 cycles is the main answer; 4 cycles (6 hours) is short.
  • This is general guidance, not medical advice.

Machine-readable copies: Markdown, JSON.

Worked examples

Each example is checked against the calculator on every build.

  1. I know my Wake-up time, Wake up at 07:00, Minutes to fall asleep 15 gives Go to bed at 23:15, Or, for 6 cycles (9 h of sleep) 21:45, Or, for 4 cycles (6 h of sleep) 00:45, In short To wake up at 7:00 AM after 5 full sleep cycles, go to bed at 11:15 PM..Source: NINDS (sleep cycles about 90 minutes); hand calculation in content.mdx
  2. I know my Wake-up time, Wake up at 06:30, Minutes to fall asleep 0 gives Go to bed at 23:00, Or, for 6 cycles (9 h of sleep) 21:30, Or, for 4 cycles (6 h of sleep) 00:30.Source: hand calculation in content.mdx
  3. I know my Bedtime, Go to bed at 22:30, Minutes to fall asleep 20 gives You fall asleep at about 22:50, Wake up at 06:20, Or, after 6 cycles (9 h of sleep) 07:50, Or, after 4 cycles (6 h of sleep) 04:50.Source: NINDS (sleep cycles about 90 minutes); hand calculation in content.mdx
  4. I know my Bedtime, Go to bed at 01:00, Minutes to fall asleep 15 gives You fall asleep at about 01:15, Wake up at 08:45.Source: hand calculation in content.mdx

How it works

A sleep cycle is taken as 90 minutes. Times are on the 24-hour clock and wrap past midnight.

If you know your wake-up time:

bedtime = wake-up time − minutes to fall asleep − cycles × 90 minutes

for 6 cycles (9 hours of sleep), 5 cycles (7 hours 30 minutes, the main answer) and 4 cycles (6 hours).

If you know your bedtime:

  • you fall asleep at = bedtime + minutes to fall asleep
  • wake-up time = you fall asleep at + cycles × 90 minutes, for 5 cycles (the main answer), 6 cycles and 4 cycles.

Minutes to fall asleep is 15 unless you change it (0 to 60), under "More options".

The one-sentence summary reads exactly, with times on the 12-hour clock:

  • Wake-up time known: "To wake up at 7:00 AM after 5 full sleep cycles, go to bed at 11:15 PM."
  • Bedtime known: "If you go to bed at 10:30 PM and fall asleep in 20 minutes, wake up at 6:20 AM after 5 full sleep cycles." With 1 minute it says "in 1 minute", and with 0 minutes it says "and fall asleep at once".

Assumptions

  • Every cycle is 90 minutes long. Real cycles run about 90 to 110 minutes, and a typical night has 4 or 5 of them (StatPearls).
  • Waking at the end of a cycle is assumed to feel easier than waking in the middle of one.
  • Five cycles is the main answer because it gives 7 hours 30 minutes of sleep, inside the 7 hours or more recommended for adults.
  • This calculator gives general guidance. It is not medical advice. Talk to a health care provider if you often have trouble sleeping or feel sleepy in the day.

Worked examples by hand

Wake up at 7:00 AM, 15 minutes to fall asleep. 7:00 AM is 420 minutes after midnight. For 5 cycles: 420 − 15 − 450 = −45, which wraps to 1,440 − 45 = 1,395 minutes = 11:15 PM. For 6 cycles: 420 − 15 − 540 = −135 → 1,305 minutes = 9:45 PM. For 4 cycles: 420 − 15 − 360 = 45 minutes = 12:45 AM.

Wake up at 6:30 AM, falling asleep at once. 390 − 450 = −60 → 11:00 PM (5 cycles); 390 − 540 = −150 → 9:30 PM (6 cycles); 390 − 360 = 30 → 12:30 AM (4 cycles).

Go to bed at 10:30 PM, 20 minutes to fall asleep. You fall asleep at 10:50 PM (1,370 minutes). 5 cycles: 1,370 + 450 = 1,820 → 1,820 − 1,440 = 380 minutes = 6:20 AM. 6 cycles: 1,370 + 540 = 1,910 → 470 = 7:50 AM. 4 cycles: 1,370 + 360 = 1,730 → 290 = 4:50 AM.

Go to bed at 1:00 AM, 15 minutes to fall asleep. You fall asleep at 1:15 AM (75 minutes). 5 cycles: 75 + 450 = 525 minutes = 8:45 AM.

Other questions people ask

What time should I go to bed?

Count back whole sleep cycles of 90 minutes from your wake-up time, then take off the time you need to fall asleep. To wake at 7:00 AM after 5 cycles (7 hours 30 minutes of sleep) with 15 minutes to fall asleep, go to bed at 11:15 PM. For 6 cycles (9 hours), go to bed at 9:45 PM.

What is a sleep cycle?

During the night you pass through light sleep, deep sleep and REM (dream) sleep, then start again. One full cycle takes about 90 to 110 minutes, and a typical night has 4 or 5 cycles. Waking at the end of a cycle, when sleep is light, is thought to feel easier than waking from deep sleep.

How much sleep do I need?

The American Academy of Sleep Medicine and the Sleep Research Society recommend 7 hours or more a night for adults aged 18 to 60. The CDC gives 7 to 9 hours for ages 61 to 64 and 7 to 8 hours for 65 and older. Five cycles (7 hours 30 minutes) or six cycles (9 hours) fit these ranges; four cycles (6 hours) is short.

How long does it take to fall asleep?

It differs from person to person and night to night. The calculator uses 15 minutes unless you change it under More options. If you often lie awake for a long time, or feel tired after a full night, talk to a health care provider.

What if I go to bed now?

Choose "Bedtime" and enter the time. The calculator adds the minutes to fall asleep, then 4, 5 and 6 cycles of 90 minutes, and shows when to set your alarm.

Are sleep cycles exactly 90 minutes?

No. 90 minutes is an average; cycles run about 90 to 110 minutes and change through the night. Treat the times as a guide and move them by 10 to 15 minutes if you often wake groggy.