Rex says
Everyday utility math — the kind you'd otherwise pull up four browser tabs for. I keep it to one clean answer.
Try a scenario
Click to load — tweak from there.Inputs
Result
Ideal bedtime
10:45 PM
One cycle later
12:15 AM
One cycle earlier
9:15 PM
Hours asleep
7.5
Total time in bed (min)
465
Sleep cycles
5
Psst — share this and help Rex grow
One click, a permanent link with your numbers baked in.
How to use this
- 1Enter wake hour (0–23).
- 2Enter wake minute.
- 3Enter minutes to fall asleep.
- 4Enter target sleep cycles.
- 5Read your ideal bedtime on the right — it updates as you type.
- 6Hit Share to keep the scenario or send it to someone.
About this calculator
A full sleep cycle runs about 90 minutes. Waking at the end of a cycle rather than mid-cycle is why six hours can feel better than seven.
Worked example
Using the values the calculator loads with:
Inputs
- Wake hour (0–23): 6
- Wake minute: 30
- Minutes to fall asleep: 15
- Target sleep cycles: 5
Results
- Ideal bedtime: 10:45 PM
- One cycle later: 12:15 AM
- One cycle earlier: 9:15 PM
- Hours asleep: 7.5
- Total time in bed (min): 465
- Sleep cycles: 5
What each field means
Inputs
- Wake hour (0–23)
- The wake hour (0–23) used in the calculation. Starts at 6 so you have a working example on load. Accepted range: 0–23.
- Wake minute
- The wake minute used in the calculation. Starts at 30 so you have a working example on load. Accepted range: 0–59.
- Minutes to fall asleep
- The minutes to fall asleep used in the calculation. Starts at 15 so you have a working example on load. Accepted range: 0–90.
- Target sleep cycles
- The target sleep cycles used in the calculation. Starts at 5 so you have a working example on load. Accepted range: 3–7.
Results
- Ideal bedtime
- Returned as a plain value and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- One cycle later
- Returned as a plain value. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- One cycle earlier
- Returned as a plain value. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Hours asleep
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Total time in bed (min)
- Returned as a whole number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Sleep cycles
- Returned as a whole number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
How does the sleep cycle calculator work?
A full sleep cycle runs about 90 minutes. Waking at the end of a cycle rather than mid-cycle is why six hours can feel better than seven. The underlying maths is: Bedtime = Wake time − (cycles × 90 minutes) − time to fall asleep.
What do I need to enter?
4 values: wake hour (0–23), wake minute, minutes to fall asleep, and target sleep cycles. Each field starts with a sensible default, so you can change one number at a time and watch the result move.
What does the ideal bedtime result mean?
It is returned as a plain value and updates live as you edit the inputs, so you can compare two or three versions of a scenario in a few seconds.
Is this calculator free, and do I need an account?
Yes, it's free, and no account is required. Nothing you type is stored on our servers — the maths runs entirely in your browser.
How accurate is the result?
It applies the standard formula exactly, so the arithmetic is precise. Estimates assume standard, average conditions — local rules, pricing, and materials vary.
Who is this tool for?
It's built for anyone doing everyday planning maths — a quick estimate that would otherwise need four browser tabs and a calculator app.
Accuracy and limitations
- Estimates assume standard, average conditions — local rules, pricing, and materials vary.
- Results are rounded for readability; add a buffer before ordering, booking, or committing.
- Double-check anything with a real cost attached against a local quote.
Related tools
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). Sleep Cycle Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/sleep-time
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/sleep-time" target="_blank" rel="noopener">Sleep Cycle Calculator — RevenueLab</a> (2026).</p>
Source: [Sleep Cycle Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/sleep-time) (2026).