Calculators
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Sleep Calculator

When to go to bed or set your alarm so you wake at the end of a sleep cycle, not in the middle of one.

  • Runs in your browser
  • No upload
  • No sign-up

Plan your sleep

Clock format
What do you want to work out?

Go to bed at

    Napping now?

    • Power nap · 20 min

      —

      Short enough to stay in light sleep, so you wake up refreshed rather than groggy.

    • Full-cycle nap · 90 min

      —

      One whole cycle, ending in light sleep. Good for catching up, but keep it before mid-afternoon.

    Alarm times include your time to fall asleep. Avoid naps of 30–60 minutes: you tend to wake from deep sleep feeling worse.

    How much sleep you need

    Recommended hours of sleep per day by age
    AgeRecommended
    Newborn (0–3 months)14–17 hours (including naps)
    Infant (4–12 months)12–16 hours (including naps)
    Toddler (1–2 years)11–14 hours (including naps)
    Preschool (3–5 years)10–13 hours (including naps)
    School age (6–12 years)9–12 hours
    Teen (13–18 years)8–10 hours
    Adult (18–60 years)7 or more hours
    Adult (61–64 years)7–9 hours
    Older adult (65+ years)7–8 hours

    Per 24 hours. Source: US Centers for Disease Control and Prevention (CDC), based on American Academy of Sleep Medicine and National Sleep Foundation guidance.

    A guide, not medical advice. Real sleep cycles vary from about 70 to 120 minutes and change through the night, so treat these times as a good starting point and adjust. If you’re often exhausted despite enough sleep, snore loudly or stop breathing in your sleep, talk to a doctor.

    About this tool

    Waking up groggy is often less about how long you slept and more about when the alarm went off. Through the night you move through cycles of light, deep and dream sleep that last around 90 minutes each. An alarm in the middle of deep sleep leaves you foggy; one at the end of a cycle, when sleep is light, feels much easier. This calculator lines your bedtime or alarm up with the ends of those cycles.

    Tell it when you need to be up and it suggests bedtimes; tell it when you are going to bed, or press “Going to bed now”, and it suggests alarm times. It allows for the time it takes you to drop off, lets you set your own cycle length between 80 and 110 minutes, and highlights the options that give the amount of sleep recommended for your age, which for most adults is five or six cycles. There are nap times too, and the age table the advice comes from.

    Times follow your device’s clock and your preferred 12 or 24-hour format, and on a night when the clocks change they already allow for the lost or extra hour. Everything runs in your browser, and nothing is sent anywhere.

    How to use Sleep Calculator

    1. Pick “I want to wake up at…”, “I’m going to bed at…” or “Going to bed now”.
    2. Enter the time, unless you chose “Going to bed now”.
    3. Set how long you usually take to fall asleep, and change the sleep cycle length or age group if you like.
    4. Choose one of the times shown; the highlighted ones give the recommended amount of sleep.
    5. Switch between 12 h and 24 h at the top, and press “Copy times” to keep the list.
    Example

    To wake at 6:30 am, allowing 15 minutes to fall asleep: go to bed at 9:15 pm for six cycles (9 hours of sleep) or 10:45 pm for five cycles (7½ hours). Later options are 12:15 am and 1:45 am.

    Features

    • Three modes: bedtimes from a wake-up time, alarm times from a bedtime, or from right now.
    • Options for three to six full sleep cycles, with hours of sleep for each.
    • Adjustable cycle length (80–110 minutes) and time to fall asleep (0–60 minutes).
    • Recommended options highlighted for nine age groups, using the CDC table of sleep needs.
    • 12 or 24-hour times, matching your language by default and remembered on this device.
    • Allows for daylight-saving clock changes overnight.
    • Power nap (20 minutes) and full-cycle nap alarm times from right now.
    • Copy the times as plain text.

    Tips and good to know

    • Ninety minutes is an average. If you often wake just before your alarm, try 80 or 85; if you still wake groggy, try 100.
    • Be honest about how long you take to fall asleep. If it is often over half an hour, keep the phone out of bed and get up for a while if sleep won’t come.
    • A regular wake-up time, weekends included, does more for your energy than any single bedtime.
    • Three cycles is a fallback for a short night, not a plan. Aim for the highlighted options most nights.
    Why 90-minute cycles?

    Studies of sleep find each cycle of light, deep and dream sleep lasts about 70 to 120 minutes, averaging around 90. Waking at the end of one, when sleep is light, usually feels easier than waking in the middle of deep sleep.

    How much sleep do I need?

    The CDC recommends 7 or more hours for adults aged 18 to 60, 7 to 9 hours from 61 to 64, 7 to 8 hours from 65, 8 to 10 hours for teenagers and more for younger children. The table on this page lists every age group.

    What if the clocks change tonight?

    The calculator works with real times on your device, so on the night the clocks go back or forward the suggested times shift to give you the right amount of sleep, and a note tells you so.

    Is anything uploaded or saved?

    Nothing is uploaded. The only thing kept is your choice of 12 or 24-hour clock, stored in your own browser.

    Is it free? Any limits?

    Yes, it is free with no sign-up and no limits.

    Does it work on a phone or offline?

    Yes. It works on iPhone, Android and computers. Once the page has loaded, the times are worked out on your device.

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