Sleep Calculator
Find suggested bedtimes or wake-up times based on sleep cycles. Many people find it easier to wake up at the end of a cycle rather than in the middle of one.
| I want to | |
| Time | |
| Fall-asleep time |
Suggested times
Your suggested times will appear here.
How it works
A typical sleep cycle lasts about 90 minutes. This calculator counts back or forward in 90-minute cycles and adds the time it usually takes you to fall asleep (about 15 minutes on average) to suggest times that may help you wake between cycles.
- 6 cycles ≈ 9 hours of sleep (often recommended for many adults)
- 5 cycles ≈ 7.5 hours
- 4 cycles ≈ 6 hours
Assumptions
Cycle length, time to fall asleep, and sleep needs vary from person to person and night to night. This is a planning guide, not a medical assessment. If you have ongoing sleep problems, consider talking with a health professional.
How it works
Sleep often moves through cycles of about 90 minutes. Waking near the end of a cycle can feel more refreshing than waking mid-cycle.
How the estimate is made
- Count back/forward in ~90-minute cycles and include time to fall asleep (commonly ~15 minutes, adjustable here).
- Many adults do well with about 4–6 cycles (roughly 6–9 hours), but needs vary.
Example
To wake at 7:00 AM with 15 minutes to fall asleep, suggested bedtimes might include ~9:45 PM (6 cycles) or ~11:15 PM (5 cycles).
General information only, not medical advice. Sleep needs vary by person and age; see a health professional for ongoing sleep concerns.
How to use the Sleep Calculator
It takes a few seconds, and every figure is calculated in your browser.
- Choose whether to work out a bedtime or a wake-up time.
- Enter the time.
- Enter how long it takes you to fall asleep.
- Press Calculate — the result appears in the dark panel beside the form.
- Use Copy, CSV, Share or Print under the result if you want to keep it.
Sleep Calculator — frequently asked questions
What formula does the Sleep Calculator use?
Count back/forward in ~90-minute cycles and include time to fall asleep (commonly ~15 minutes, adjustable here). Many adults do well with about 4–6 cycles (roughly 6–9 hours), but needs vary.
How does the Sleep Calculator work?
A typical sleep cycle lasts about 90 minutes. This calculator counts back or forward in 90-minute cycles and adds the time it usually takes you to fall asleep (about 15 minutes on average) to suggest times that may help you wake between cycles. 6 cycles ≈ 9 hours of sleep (often recommended for many adults) 5 cycles ≈ 7.5 hours 4 cycles ≈ 6 hours
What assumptions and limitations should I know about?
Cycle length, time to fall asleep, and sleep needs vary from person to person and night to night. This is a planning guide, not a medical assessment. If you have ongoing sleep problems, consider talking with a health professional.
Can you walk through a worked example?
To wake at 7:00 AM with 15 minutes to fall asleep, suggested bedtimes might include ~9:45 PM (6 cycles) or ~11:15 PM (5 cycles).
Last updated 10 November 2026 · Formula, worked example and assumptions are documented above, and every result is calculated in your browser.