Sleep Cycle Calculator

Wake up refreshed instead of groggy: pick a wake-up time and get the best bedtimes — or go to bed now and see the ideal wake-up times — based on 90-minute sleep cycles.

All calculations run locally in your browser.

How to use Sleep Cycle Calculator

  1. Choose “I want to wake up at…” and pick a time, or choose “I’m going to bed now”.
  2. The calculator adds ~15 minutes to fall asleep.
  3. It then lists bedtimes or wake-up times for 4, 5 and 6 full cycles.
  4. Aim for 5–6 cycles (7.5–9 hours) for the best rest.

About this tool

Sleep runs in roughly 90-minute cycles. Waking mid-cycle is what makes mornings feel terrible, while waking at the end of a cycle feels natural.

The calculator works backwards from your alarm (adding the average 15 minutes it takes to fall asleep) or forwards from your bedtime, and shows every cycle-friendly option.

When to use it: choosing bedtimes or alarms so you wake between cycles, not during one.

Frequently asked questions

How many cycles do I need?
Most adults do best with 5–6 cycles (7.5–9 hours). Four cycles (6 hours) is the common minimum for a short night.
Why 90 minutes per cycle?
A full pass through light sleep, deep sleep and REM averages about 90 minutes, although individuals vary a little in practice.
Why are 15 minutes added?
That is the average time people take to fall asleep. If you usually take longer, simply allow for the difference.
Do naps follow cycles too?
Yes — about 20 minutes, or a full 90, avoids waking mid-cycle, which is what causes nap grogginess.
Is this medical advice?
No — it is a planning aid based on the common cycle model. Persistent sleep problems deserve professional attention.
Is it useful for shift workers?
Very — anchor the “wake up at” mode to your real alarm time and let it suggest bedtimes whenever your rotation allows sleep.

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How to use Sleep Cycle Calculator

Enter the required values into the Sleep Cycle Calculator fields. The calculation updates as you adjust inputs. Use the result for planning, comparison, or documentation.

Practical benefits

Frequently asked questions

Is this tool free to use?
Yes. Sleep Cycle Calculator is fully free with no account or subscription required.
Does it upload my files?
No. All processing occurs locally within your browser session.
Can I use this for professional projects?
Yes, the tool is designed for both casual and professional use. Always verify critical outputs.