Skip to content
VitalsNook
Menu
Every tool runs in your browser. Your files never leave your device.

Sleep calculator

Pick the time you need to wake up to see bedtimes that end on a full sleep cycle, or pick a bedtime to see good times to wake, with the hours of sleep each gives and the usual time it takes to fall asleep.

Start with

When your alarm goes off.

15 is a common guess. Use what’s usual for you.

Real cycles last about 80 to 100 minutes and change through the night, so 90 is a rule of thumb, not a measurement of your sleep.

Go to bed at
10:45 PM
Asleep by about 11:00 PM, then 5 cycles of 90 minutes: 7 h 30 min of sleep before 6:30 AM. For 6 cycles (9 h), go to bed at 9:15 PM.

Bedtimes for a 6:30 AM wake-up

  • 9:15 PM
    6 cycles · 9 h of sleep
    7+ hours
  • 10:45 PM
    5 cycles · 7 h 30 min of sleep · suggested
    7+ hours
  • 12:15 AM
    4 cycles · 6 h of sleep
    Under 7 hours
  • 1:45 AM
    3 cycles · 4 h 30 min of sleep
    Under 7 hours

Adults need 7 or more hours a night (AASM and Sleep Research Society, 2015). Teens and children need more.

A rule-of-thumb estimate, not medical advice. If you regularly struggle to fall or stay asleep, snore loudly or feel tired after enough hours in bed, talk to your doctor.

  • Free, no sign-up
  • Works on phone and desktop

How to find your best bedtime

  1. 1

    Choose whether you know your wake-up time or your bedtime.

  2. 2

    Enter the time, or press Now if you’re heading to bed.

  3. 3

    Adjust the time to fall asleep if you usually take longer or shorter than 15 minutes.

  4. 4

    Pick one of the suggested times. Options with 7 or more hours of sleep are marked.

Features

  • Whole sleep cycles

    Bedtimes and alarms that land at the end of a roughly 90-minute cycle, when waking tends to be easier.

  • Time to fall asleep

    Allows 15 minutes to drift off by default. Change it to match how long you usually take.

  • Enough hours

    Highlights options that give adults the 7 or more hours sleep experts recommend, not just a tidy cycle count.

  • Private

    Runs on your device. The current time is read only when you press Now.

How the sleep calculator works

Through the night you move through cycles of lighter sleep, deep (slow-wave) sleep and REM sleep, when most dreaming happens. The National Heart, Lung, and Blood Institute says each cycle lasts about 80 to 100 minutes and most people have four to six a night. Waking from deep sleep tends to leave you groggy, so the idea is to time your alarm for the end of a cycle. The calculator uses:

  • Bedtime = wake-up time − (number of cycles × 90 minutes) − time to fall asleep.
  • Wake-up time = bedtime + time to fall asleep + (number of cycles × 90 minutes).

It lists three to six cycles and suggests the fewest that still give you 7 hours of sleep. You can change both the time to fall asleep (default 15 minutes) and the cycle length.

CyclesHours of sleepTime in bed
34 h 30 min4 h 45 min
46 h6 h 15 min
57 h 30 min7 h 45 min
69 h9 h 15 min

Time in bed includes 15 minutes to fall asleep, with 90-minute cycles.

Worked examples

  • Up at 6:30 AM for work: the bedtimes are 9:15 PM, 10:45 PM, 12:15 AM or 1:45 AM. The suggested one is 10:45 PM: asleep by about 11:00 PM, five cycles, 7 h 30 min of sleep.
  • In bed at 11:00 PM: good times to wake are 3:45 AM, 5:15 AM, 6:45 AM or 8:15 AM. 6:45 AM is the first that gives 7 or more hours.
  • Slow to drop off? If you usually take 30 minutes and need to be up at 7:00 AM, the bedtimes move to 9:30 PM, 11:00 PM, 12:30 AM or 2:00 AM.
  • Longer cycles: with 100-minute cycles instead of 90, the same 7:00 AM alarm gives 8:45 PM, 10:25 PM, 12:05 AM or 1:45 AM. The gap grows with every cycle, which is why the 90-minute rule is only a guide.

How much sleep do you need?

The hours matter more than the cycles. These are the CDC’s recommendations, drawn from the American Academy of Sleep Medicine’s consensus statements for children and adults and, for newborns and adults over 60, from the National Sleep Foundation:

Age groupAgeRecommended sleep per day
Newborn0–3 months14–17 hours
Infant4–12 months12–16 hours, including naps
Toddler1–2 years11–14 hours, including naps
Preschool3–5 years10–13 hours, including naps
School age6–12 years9–12 hours
Teen13–17 years8–10 hours
Adult18–60 years7 or more hours
Adult61–64 years7–9 hours
Adult65 and older7–8 hours

For a teenager who has to be up at 7:00 AM, eight to ten hours means a bedtime of 9:45 PM for six cycles, or a little later; the five-cycle option at 11:15 PM gives only 7½ hours. For adults, the AASM and Sleep Research Society add that sleeping more than 9 hours can be right for young adults, people recovering from lost sleep and people who are ill.

What the calculator can’t tell you

The 90-minute cycle is a rule of thumb. The NHLBI gives a range of 80 to 100 minutes and a StatPearls review 90 to 110, cycles change through the night, and nobody falls asleep at exactly the same speed every night. Across five cycles, a 10-minute difference per cycle adds up to almost an hour. The calculator also can’t know whether your sleep is good quality: if you snore loudly, wake up often or feel tired after enough hours in bed, a timetable won’t fix that.

What helps most, according to the American Academy of Sleep Medicine’s healthy sleep habits, is a steady routine: get up at the same time every day, including weekends, set a bedtime early enough for at least 7 to 8 hours, and if you can’t fall asleep after about 20 minutes, get up and do something quiet in dim light. The CDC adds turning screens off at least 30 minutes before bed and avoiding caffeine in the afternoon and alcohol before bedtime.

Sleep and fitness go together: see your training intensity with the heart rate zone calculator, plan runs with the pace calculator, or check your daily calories with the TDEE calculator.

Sources

This calculator gives rule-of-thumb timings, not medical advice. If you regularly have trouble falling or staying asleep, or feel sleepy during the day despite enough time in bed, talk to your doctor, who can check for common sleep disorders such as insomnia and sleep apnea.

Frequently asked questions

What time should I go to bed to wake up at 6 AM?

With 15 minutes to fall asleep, aim for 10:15 PM for five 90-minute cycles (7 h 30 min of sleep) or 8:45 PM for six (9 h). Going to bed at 11:45 PM gives four cycles, only 6 h: less than adults need.

How many hours of sleep do I need?

Adults need 7 or more hours a night on a regular basis, according to the American Academy of Sleep Medicine and the Sleep Research Society. Teenagers need 8 to 10 hours, school-age children 9 to 12, and younger children more, including naps.

How long is a sleep cycle?

About 80 to 100 minutes, according to the National Heart, Lung, and Blood Institute, and most people go through four to six cycles a night. 90 minutes is a convenient average, but cycles vary between people and through the night: deep sleep comes mostly early on and dreaming (REM) sleep later.

Is 6 hours of sleep enough?

Not for most adults on a regular basis. The 2015 consensus found that sleeping less than 7 hours a night regularly is linked to weight gain, diabetes, high blood pressure, heart disease, depression and more accidents. Six hours fits four cycles neatly, but the number of hours matters more than ending on a cycle.

What if I can’t fall asleep?

The American Academy of Sleep Medicine suggests getting out of bed if you haven’t fallen asleep after about 20 minutes and doing something quiet in low light, without screens, until you feel sleepy. If it happens most nights, talk to your doctor: insomnia is one of the common sleep disorders a doctor can help with.

Does waking up between sleep cycles really help?

It’s a rule of thumb rather than a precise method. Being woken from deep sleep can leave you groggy for 30 minutes to an hour, and waking near the end of a cycle avoids that. But because cycles aren’t exactly 90 minutes, the timing drifts over a night, so treat the suggestions as a guide and see what works for you.

More free tools