Sleep cycle
calculator
A little room for rest.
A planning estimate, not a prediction of sleep stages.
How to use the sleep cycle calculator
Sleep Cycle Calculator is a free English-language tool for planning bedtime or wake-up time. Enter a clock time and your time to fall asleep, then compare 8-hour, 7.5-hour, and 9-hour sleep plans. Calculations run in your browser, with no account required.
Start with your local time
Your current time is filled in as bedtime. Edit it, or choose “Wake up at” to work backward.
Allow time to fall asleep
Start with a 15-minute allowance, or open preferences to adjust it and choose 12- or 24-hour time.
Compare your sleep plans
Press Calculate to see the 8-hour default alongside 7.5- and 9-hour plans. Check each time and day label.
- Two modes: work forward from bedtime or backward from a wake-up time.
- Three plans appear together: 8 hours (default), 7.5 hours, and 9 hours of sleep.
- Time to fall asleep defaults to 15 minutes and accepts 0–120 whole minutes.
- Use 12- or 24-hour time; preferences are saved only in this browser.
- The 7.5- and 9-hour cycle labels assume 90 minutes per cycle; actual sleep stages are not measured.
Published by Sleep cycle calculator · Updated
How are sleep times calculated?
A bedtime calculator makes space in your schedule. Your body takes it from there.
This sleep calculator starts with the time you have, then adds or subtracts each sleep duration and an allowance for falling asleep. The 8-hour plan is highlighted by default, alongside 7.5- and 9-hour alternatives.
Sleep cycles vary. They are not a fixed 90-minute timer, and this tool cannot tell when you will be in light, deep, or REM sleep. It does not account for waking during the night. Timing a cycle is no substitute for enough sleep.
For background, read NHLBI’s guide to sleep stages and CDC’s sleep guidance. This tool is for general planning, not medical advice.
What time should I go to bed to wake up at 7 AM?
For a 7:00 AM wake-up time, these plans include 15 minutes to fall asleep. All bedtimes are on the previous day. Cycle counts are approximate, based on 90 minutes per cycle.
| Sleep | Cycle estimate | Bedtime |
|---|---|---|
| 8 hours (default) | Not used | 10:45 PMPrevious day |
| 7.5 hours | About 5 | 11:15 PMPrevious day |
| 9 hours | About 6 | 9:45 PMPrevious day |
Sleep calculator questions
How does this sleep cycle calculator work?
Sleep Cycle Calculator adds or subtracts a sleep duration and your allowance for falling asleep. Enter your bedtime or wake-up time and press Calculate to see all three plans: 8 hours (default), 7.5 hours, and 9 hours. For example, a 7:00 AM wake-up time with 8 hours of sleep and a 15-minute allowance gives a bedtime of 10:45 PM the previous day.
Are sleep cycles always 90 minutes?
No. NHLBI describes cycles of about 80–100 minutes, and sleep stages change through the night. The 7.5- and 9-hour plans show about 5 and 6 cycles by dividing their duration by 90 minutes. Those labels are rough estimates, not measured cycles or predictions of when you will wake refreshed.
Why is 8 hours the default plan?
Eight hours is a simple planning default, not a personal prescription. CDC recommends at least 7 hours for adults aged 18–60; needs differ with age and individual circumstances. The 7.5- and 9-hour plans appear alongside it for comparison. A shorter night is not made healthier by trying to time a sleep cycle.
Does the result include time to fall asleep?
Yes. Each plan adds time to fall asleep on top of its sleep duration. The allowance defaults to 15 minutes and can be set from 0 to 120 whole minutes. With 8 hours of sleep and a 15-minute allowance, the plan leaves 8 hours 15 minutes between bedtime and waking. The allowance is your estimate, not a measurement of your sleep.
What do the day labels and local times mean?
“Previous day,” “Same day,” and “Next day” are relative to your starting time. On each visit, bedtime is captured from your device to the minute and keeps its date for daylight saving adjustments. It does not tick forward while you plan. Editing the clock uses a typical day without a date, so manually entered times do not adjust for daylight saving changes.
Is Sleep Cycle Calculator free, and what does it save?
Sleep Cycle Calculator is free and needs no account. Calculations stay in your browser. Only your time to fall asleep, time format, and preferred wake-up time are saved locally. Bedtime starts fresh from your device clock on each visit. There is no sleep history. Clear this site’s browser data to remove saved settings.