Sleep Cycle Calculator logo

Prescosoft

Sleep Cycle Calculator

 Open Tool
100% in your browser — no uploads

Sleep Cycle
Calculator

Wake up refreshed by aligning your alarm with the end of a 90-minute sleep cycle. Best bedtimes, best wake times, or a quick "sleep now" — all calculated privately on your device.

Find My Times Free forever · No account · No watermark
Nothing is uploaded 90-min cycle science 4–7 cycle options No account needed

Get in bed 15 minutes before the listed sleep start — the calculator adds the fall-asleep buffer.

How it works

Simple 90-minute cycle math, transparent and local.

1

Pick your anchor

A wake time, a bedtime, or "now." The calculator works backward or forward from your anchor in 90-minute blocks.

2

Count whole cycles

You get 4, 5, 6, and 7-cycle options with total time in bed. A 15-minute fall-asleep buffer is added so your first cycle actually starts on time.

3

Wake at cycle end

Alarms that land at the end of a cycle catch you in lighter sleep — the classic trick for waking up less groggy.

Why Prescosoft Sleep Cycle Calculator

  • Your sleep schedule never leaves your device — no account, no sync, no ads.
  • Blazing fast: results appear instantly, no signup wall.
  • Transparent math: 90-minute cycles, 15-minute buffer, 4–7 options shown.
  • Works offline after the page loads.

Typical online sleep calculators

  • sleepyti.me was bought out and buried in bloated, ad-stuffed pages — users actively search for replacements.
  • Apps push accounts, subscriptions, and cloud sync for a 30-second calculation.
  • Many hide the math and show one "magic" time with no cycle options.
  • Trackers and telemetry on pages that claim to be about rest.

Who is this for?

⏰

Morning people

Need to be up at a fixed hour for work or school? Get the bedtimes that land your alarm at a cycle boundary — and the one to pick for tonight.

🌙

Night owls

Going to bed at your natural late hour? See which wake times complete whole cycles — and how many hours each option actually buys you.

🔄

Shift workers & travelers

Odd schedules wreck cycle alignment. The "sleep now" mode tells you the best wake windows for whatever time you finally hit the pillow.

Frequently Asked Questions

How does a sleep cycle calculator work?
Adults typically sleep in cycles of about 90 minutes, moving through light sleep, deep sleep, and REM sleep before the cycle repeats. Waking up mid-cycle — especially during deep sleep — is why you can feel groggy after 9 hours but fine after 7.5. The calculator works backward or forward in 90-minute blocks: pick a wake time and it subtracts whole cycles to find bedtimes, or pick a bedtime and it adds whole cycles to find wake times. A 15-minute fall-asleep buffer is included.
What are the best bedtimes if I need to wake at 7 AM?
Working back from 7:00 AM in 90-minute cycles with a 15-minute buffer: 9:45 PM (6 cycles, 9.25h in bed), 11:15 PM (5 cycles, 7.75h), or 12:45 AM (4 cycles, 6.25h). These times align your alarm with the end of a cycle so you wake during lighter sleep. Pick the one closest to your natural bedtime — consistency matters more than the exact minute.
Is the 90-minute sleep cycle real?
The 90-minute ultradian rhythm is a well-documented average, but real cycles vary from person to person and night to night (typically 70-120 minutes). That's why the calculator shows a range of options rather than one "magic" time, and why waking at the end of a cycle is a heuristic that helps many people feel better — not a guarantee. If you track your sleep with a wearable, use your own average cycle length for even better results.
Should I include time to fall asleep?
Yes. Most people take 10-20 minutes to fall asleep, so the calculator adds a 15-minute buffer: the "get in bed" time is 15 minutes before the sleep-start time that begins your first cycle. If you know you take longer, shift everything 10-15 minutes earlier; if you fall asleep instantly, you can ignore the buffer.
How many sleep cycles do I need?
Most adults feel best with 5-6 full cycles (7.5-9 hours in bed). Four cycles (6 hours) is the minimum most people can sustain; seven cycles (10.5 hours) is more than most need and can be hard to achieve. The calculator shows 4-7 cycle options so you can match your schedule, then aim for the same count most nights for consistency.
Is my data saved or uploaded?
No. Everything is computed locally in your browser with plain JavaScript. Your times are never uploaded, stored, or transmitted anywhere, and the tool works offline after the page loads. There is no account, no tracking, and no server involved.

Related guides

Magnesium Sleep Lab

Magnesium for Better Sleep: Types, Dosage & Timing

A science-backed look at the supplement everyone asks about — what works, what doesn't, and how to track it.

Read guide PureFocus Timer

The Pomodoro Technique: Focus Better in 25-Minute Blocks

Rest and focus work on rhythms too — here's the productivity rhythm that pairs with better sleep.

Read guide

More Prescosoft tools

🌙

Magnesium Sleep Lab

Track sleep wellness.
⏱️

PureFocus Timer

Pomodoro focus timer.
🌍

Time Zone Planner

Plan across time zones.
📈

Body Progress Tracker

Track health progress.

Find your best bedtime tonight

90-minute cycle timing, computed privately on your device. Your sleep schedule stays yours.

Find My Times Now