Health & Fitness
Sleep Calculator
Sleep — sleep Calculator works in roughly 90-minute sleep cycles, counting back or forward from your chosen wake or bedtime and allowing about 15 minutes to fall asleep. This page runs that same calculation on your numbers, in your browser: no signup, no uploads, nothing stored.
From a bedtime or wake-up time to plan around, Sleep Calculator computes the best times to fall asleep or wake via 90-minute sleep-cycle timing. No accounts, no uploads — just an instant way to time sleep around 90-minute cycles.
About this calculator
Sleep Calculator works in roughly 90-minute sleep cycles, counting back or forward from your chosen wake or bedtime and allowing about 15 minutes to fall asleep. That is the whole of the calculation — the mistakes happen in the inputs. It matters when you want a quick screening number before deciding whether a habit, plan or measurement deserves a closer look. Worked example: To wake at 06:30 with ~90-minute sleep cycles, good bedtimes are about 21:30, 23:00 or 00:30 (5–6 full cycles). Use the calculator with your own figures; it runs entirely on your device.
How to use
- Choose whether you are planning a wake time or a bedtime.
- Enter that time using the time picker.
- Press Calculate to see cycle-aligned suggestions.
- Pick the option that gives you enough total sleep.
Why use Sleep Calculator
Fast
Calculations run in your browser. No round trip to a server.
Private
Your inputs never leave your device. Nothing is uploaded.
Free
No signup, no paywall, no ads-in-results, no watermarks.
Educational
Uses common estimation formulas for educational purposes. Results are not medical advice and should not replace professional guidance.
Mobile-ready
Optimised for phones, tablets, and desktops alike.
Transparent
Clear about formulas used and their limits, with disclaimers where they matter.
Common uses
Sleep to wake between sleep cycles
Use it for fixing a sleep schedule
Sleep as a general sleep-routine guide
Use it when planning a nap
Use it for shift-work and travel timing
Use it when winding down for the night
Technical notes
Sleep Calculator works in roughly 90-minute sleep cycles, counting back or forward from your chosen wake or bedtime and allowing about 15 minutes to fall asleep.
A general sleep-timing guide based on an average cycle length; everyone differs, so adjust it to how you actually feel.
Results are rounded for display; the underlying calculation keeps full precision.
FAQ
How does the Sleep Calculator pick times?
It works in roughly 90-minute cycles and adds about 14 minutes to fall asleep, then lists options that let you wake near the end of a cycle.
Should I plan by bedtime or wake time?
If your morning is fixed, plan by wake time to find bedtimes. If your evening is fixed, set a bedtime to see good wake times.
How many sleep cycles do I need?
Most adults do well with five to six cycles, about 7.5 to 9 hours, though individual needs vary with age and lifestyle.
Does the Sleep Calculator send my data to a server?
No. The Sleep Calculator runs entirely in your browser — your inputs never leave your device, and nothing is uploaded or stored.
Worked example
To wake at 06:30 with ~90-minute sleep cycles, good bedtimes are about 21:30, 23:00 or 00:30 (5–6 full cycles).