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
9 hrs sleep — bed at
21:46
7.5 hrs sleep — bed at
23:16
6 hrs sleep — bed at
00:46
Psst — share this and help Rex grow
One click, a permanent link with your numbers baked in.
How to use this
- 1Enter wake time (hh:mm, 24h).
- 2Enter mins to fall asleep.
- 3Read your 9 hrs sleep — bed at on the right — it updates as you type.
- 4Hit Share to keep the scenario or send it to someone.
About this calculator
Sleep happens in ~90-minute cycles. This suggests bedtimes that end on a cycle boundary so you wake refreshed.
Worked example
Using the values the calculator loads with:
Inputs
- Wake time (HH:MM, 24h): 07:00
- Mins to fall asleep: 14
Results
- 9 hrs sleep — bed at: 21:46
- 7.5 hrs sleep — bed at: 23:16
- 6 hrs sleep — bed at: 00:46
What each field means
Inputs
- Wake time (HH:MM, 24h)
- Free text used in the calculation. Defaults to "07:00".
- Mins to fall asleep
- The mins to fall asleep used in the calculation. Starts at 14 so you have a working example on load.
Results
- 9 hrs sleep — bed at
- 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.
- 7.5 hrs sleep — bed at
- Returned as a plain value. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- 6 hrs sleep — bed at
- Returned as a plain value. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
How does the sleep cycle calculator work?
Sleep happens in ~90-minute cycles. This suggests bedtimes that end on a cycle boundary so you wake refreshed.
What do I need to enter?
2 values: wake time (hh:mm, 24h), and mins to fall asleep. Each field starts with a sensible default, so you can change one number at a time and watch the result move.
What does the 9 hrs sleep — bed at 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 Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/sleep
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/sleep" target="_blank" rel="noopener">Sleep Calculator — RevenueLab</a> (2026).</p>
Source: [Sleep Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/sleep) (2026).