# 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.

Content reviewed: 2026-11-09.

Source: https://sleepcyclecalculator.net/

## Product facts

- 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.

## How to use the calculator

1. **Start with your local time.** Your current time is filled in as bedtime. Edit it, or choose “Wake up at” to work backward.
2. **Allow time to fall asleep.** Start with a 15-minute allowance, or open preferences to adjust it and choose 12- or 24-hour time.
3. **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.

## 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 duration | Cycle estimate | Bedtime | Day |
| --- | --- | --- | --- |
| 8 hours (default) | Not used | 10:45 PM | Previous day |
| 7.5 hours | About 5 | 11:15 PM | Previous day |
| 9 hours | About 6 | 9:45 PM | Previous day |

## Questions and answers

### 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.

## Further reading cited on the website

- [NHLBI · Sleep phases and stages](https://www.nhlbi.nih.gov/health/sleep/stages-of-sleep)
- [CDC · About sleep](https://www.cdc.gov/sleep/about/)

## Public pages

- [Calculator and guide](https://sleepcyclecalculator.net/): Find bedtime or wake-up times with our free sleep cycle calculator. Compare 8, 7.5, and 9 hours of sleep, including time to fall asleep.
- [About](https://sleepcyclecalculator.net/about): A simple, free sleep calculator for planning bedtime and wake-up time. Learn how it works, what it includes, and what it cannot predict.
- [Privacy](https://sleepcyclecalculator.net/privacy): How Sleep Cycle Calculator handles local preferences, browser calculations, hosting requests, and optional future integrations.