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DayUtils

Sleep Calculator – Best Time to Sleep and Wake Up

Work out what time to go to bed so you wake up at the end of a sleep cycle, or what time to set your alarm if you go to bed now. The calculator uses 90-minute sleep cycles and adds the time it takes you to fall asleep.

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How to use the sleep calculator

  1. Choose whether you want to wake up at a set time or are going to bed at a set time.
  2. Enter the time.
  3. Adjust how long it usually takes you to fall asleep (15 minutes by default).

You’ll see the best times to go to bed — or to set your alarm — for 6, 5, 4 and 3 full sleep cycles, with the total sleep each gives. Times are shown in your usual 12-hour or 24-hour format.

How the times are worked out

Bedtime = Wake-up time − (cycles × 90 minutes) − time to fall asleep
Wake-up time = Bedtime + time to fall asleep + (cycles × 90 minutes)

Worked example: wake up at 7:00 am

Go to bedCyclesSleep
9:45 pm69 hours
11:15 pm57.5 hours
12:45 am46 hours
2:15 am34.5 hours

Five or six cycles fit the 7 to 9 hours most adults need.

The stages of sleep

  • Light sleep (N1 and N2) — you drift off and your heart rate and temperature drop. About half the night is spent here.
  • Deep sleep (N3) — the body repairs tissue and strengthens the immune system. Most deep sleep happens in the first half of the night.
  • REM sleep — the brain is active and most dreaming happens. REM periods get longer towards morning and help memory and mood.

Tips for better sleep

  • Keep a regular schedule, even at weekends.
  • Get daylight in the morning to set your body clock.
  • Avoid caffeine in the 6 to 8 hours before bed.
  • Keep the bedroom cool, dark and quiet.
  • Put screens away for 30 to 60 minutes before sleep.
  • Limit alcohol — it helps you fall asleep but disturbs sleep later in the night.

When to get help

If you regularly struggle to fall or stay asleep, snore loudly, stop breathing during sleep or feel very sleepy during the day, talk to a doctor. Conditions such as insomnia and sleep apnoea are common and treatable. This calculator gives general guidance only — see our disclaimer. Staying hydrated and active also helps sleep; see the water intake calculator and the heart rate zone calculator.

Frequently asked questions

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

For six full 90-minute cycles plus 15 minutes to fall asleep, go to bed at 9:45 pm. For five cycles, 11:15 pm. Both let you wake at the end of a cycle rather than in the middle of deep sleep.

What is a sleep cycle?

During the night you move through stages of light sleep, deep sleep and REM (dreaming) sleep. One full cycle takes roughly 90 minutes on average, though it varies from about 70 to 120 minutes between people and through the night.

Why do I feel groggy even after enough sleep?

Waking from deep sleep can leave you feeling heavy and confused for a while — called sleep inertia. Timing your alarm to the end of a cycle can help, but getting enough total sleep matters most.

How much sleep do adults need?

Most adults need 7 to 9 hours a night. Teenagers need about 8 to 10 hours, and younger children more.

How long does it take to fall asleep?

For most healthy adults, about 10 to 20 minutes. The calculator uses 15 minutes by default — change it to match you.

Is it better to nap for 20 or 90 minutes?

A short nap of 10 to 20 minutes usually avoids deep sleep and leaves you refreshed. A 90-minute nap completes a full cycle. Naps of 30 to 60 minutes are more likely to leave you groggy.

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