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Sleep Cycle Calculator — Best Bedtime & Wake-Up Time (90-Minute REM Cycles)

Sleep cycle calculator — 90-minute REM cycles. Find best bedtime if you must wake at X, or best wake time if you sleep at Y.

  • Runs locally
  • Category Calculator
  • Best for Getting a realistic range before a purchase, plan, workout, or schedule decision.

Cycles run ~90 min. Waking between cycles dodges sleep inertia even if total sleep is shorter.

Best bedtimes
3 cycles
01:46
4.7 h in bed
short
4 cycles
00:16
6.2 h in bed
recommended
5 cycles
22:46
7.7 h in bed
recommended
6 cycles
21:16
9.2 h in bed
full rest
Quick scenarios
Nap mode (skip cycles)

For naps under 30 minutes, ignore the cycle math — you want to wake from stage 2, not finish a full cycle. Set a 20-minute alarm and get up the moment it rings.

Recommended sleep by age (NSF / WHO / CDC)
AgeHours
0–3 mo14–17 h
4–11 mo12–15 h
1–2 y11–14 h
3–5 y10–13 h
6–13 y9–11 h
14–17 y8–10 h
18–64 y7–9 h
65+ y7–8 h
Quick tips
  • Last coffee 6–8 h before bedtime — caffeine half-life is ~5 h.
  • Dim and warm your screens 1–2 h before bed; blue light pushes sleep onset later.
  • 20-min naps stay in N2 (no grogginess). Avoid 30–60 min — that lands you in N3.
  • A consistent wake time matters more than a consistent bedtime for circadian rhythm.
  • If you wake before the alarm, get up — going back to sleep often lands you in N3 and the alarm hurts.

100% client-side. Your times never leave this page.

What this tool does

Free sleep-cycle calculator built on the 90-minute REM cycle rule. Two modes: (1) "I must wake up at X" — gives you 5–6 best bedtimes that let you finish full 90-minute cycles, so the alarm rings between cycles instead of in the middle of deep sleep (which is what makes you feel wrecked even after 8 hours); (2) "I'm going to sleep at Y" — gives you 5–6 best wake-up times the other direction. The calculator adds 14 minutes of fall-asleep latency by default (sleep-onset latency from the Pittsburgh Sleep Quality Index for healthy adults) — slide it up to 25–30 if you doomscroll in bed, down to 5 if you fall asleep the moment your head hits the pillow. Recommended total sleep by age follows the joint WHO / CDC / NSF (National Sleep Foundation) consensus: school kids 9–11 h, teens 8–10 h, adults 7–9 h, 65+ 7–8 h. Quick presets cover the cases people actually search: must-wake-at-6:30, 20-minute power nap (skip cycle math, stay in stage-2), 90-minute lunch nap (one full cycle so you don't wake mid-deep-sleep), and "exam morning — I need to be sharp at 8 AM." All math runs in your browser. No date, no time, no input is ever uploaded.

Tool details

Input
Numbers
The page exposes text boxes, numeric controls, file pickers, or structured inputs depending on the tool.
Output
Live result
The result area focuses on usable output, with copy, download, or preview actions when supported.
Privacy
Browser-side processing
The main tool logic does not call an external API, so inputs normally stay in the current tab.
Save / share
No account required
Open the page and use it; whether results survive refresh depends on the tool.
Performance budget
Initial JS <= 15 KB
No WASM budget is declared, keeping the tool quick to open on mobile.
Best fit
Calculator · Student
Category and role tags drive related tools, internal links, and quick fit checks.

How to use

  1. 1. Input

    Paste or drop your content into the tool panel.

  2. 2. Process

    Click the button. All processing is local in your browser.

  3. 3. Copy / Download

    Copy the result or download to disk in one click.

How Sleep Cycle Calculator fits into your work

Use it for fast estimates, comparisons, and planning numbers before you make the final call.

Calculation jobs

  • Getting a realistic range before a purchase, plan, workout, or schedule decision.
  • Comparing scenarios by changing one input at a time.
  • Turning rough assumptions into a number you can discuss.

Calculation checks

  • Double-check units, dates, rates, and rounding assumptions.
  • Treat health, finance, tax, and legal outputs as planning aids, not professional advice.
  • Save the inputs that produced an important result so you can reproduce it later.

Good next steps

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FAQ

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Made by Toolora · 100% client-side · Updated 2026-05-29