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Sleep Calculator

Choose whether you want to work back from a wake-up time or forward from a bedtime. The calculator adds your estimated time to fall asleep and shows options for four, five and six 90-minute sleep cycles, including times that fall on the previous or next day. Scheduling estimates only, calculated locally.

Back

1. Your schedule

90-minute cycles
Plan from

Default fall-asleep time: 15 minutes. Each cycle is assumed to last 90 minutes.

2. Suggested times

—
Enter a wake-up time, then press Suggest bedtimes.
About this tool

About Sleep Calculator

Sleep Calculator suggests bedtimes for a chosen wake-up time, or wake-up times for a chosen bedtime, based on 90-minute sleep cycles. It adds an adjustable allowance for the time it takes to fall asleep, lists four-, five- and six-cycle options, and labels any time that falls on the previous or next day.

Working out bedtimes backwards across midnight is fiddly, especially once you add time to fall asleep. This calculator does the clock arithmetic for you in 12-hour or 24-hour format and explains the assumptions, so you can plan a schedule while remembering that real sleep cycles vary.

How to use

Step by step

  1. Choose whether to plan from a wake-up time or from a bedtime.
  2. Enter the time.
  3. Adjust the time to fall asleep if 15 minutes does not suit you.
  4. Choose 12-hour or 24-hour display.
  5. Press the suggest button to see the options, then copy or download the schedule.
Key features

What it offers

  • Two modes: suggested bedtimes or suggested wake-up times
  • Four, five and six 90-minute cycle options
  • Adjustable fall-asleep time from 0 to 120 minutes, defaulting to 15
  • Previous-day and next-day labels for times around midnight
  • 12-hour and 24-hour display, used in summaries too
  • Sleep duration and total time in bed for every option
Best practices

Tips for best results

  • Set the fall-asleep time to what is typical for you.
  • Use the options as a starting schedule and adjust to how you feel.
  • Keep similar bed and wake times across the week where possible.
  • Remember that cycle length varies, so exact timing is an estimate.
Benefits

Why people use it

Midnight-safe

Times that cross midnight are clearly labelled.

Your format

Switch between 12-hour and 24-hour time.

Private

Calculated in your browser and never stored.

FAQ

Common questions

It treats sleep as a series of cycles of about 90 minutes. In wake-up mode it counts back from your wake-up time by your fall-asleep time plus four, five or six cycles to suggest bedtimes. In bedtime mode it counts forward from your bedtime to suggest wake-up times.
Sleep moves through light, deep and REM stages in repeating cycles that are often described as lasting roughly 90 minutes on average. Real cycles vary from about 70 to 120 minutes between people and through the night, so the times shown are scheduling estimates, not precise predictions.
It is how long you usually take to fall asleep after going to bed. The default is 15 minutes; you can enter any whole number from 0 to 120 minutes. It is added to each option, so a bedtime is the time you get into bed, not the time you fall asleep.
When a suggested time crosses midnight, it is labelled relative to the time you entered. For example, a 07:00 wake-up time often gives bedtimes on the previous day, such as 21:45, and a 23:30 bedtime gives wake-up times on the next day.
Yes. Choose 12-hour (for example 10:45 PM) or 24-hour (22:45) display. The Copy and Download summaries use the same format as the times on screen.
The calculator does not recommend a specific number; it simply lists the four-, five- and six-cycle options (6, 7.5 and 9 hours of sleep). Sleep needs differ between people. This is a general educational estimate, not medical advice, diagnosis or treatment.
No. The calculation runs in your browser and nothing is stored or sent anywhere.

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Private by design

This runs entirely in your browser

No file or text you enter here is uploaded. Encoding and decoding happen on your device using native browser APIs — close the tab and nothing remains on a server.

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