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Free · No signup · Instant results · Updated 2026-09-17

Sleep Calculator

Answer: Sleep cycle planning targets 90-minute REM/NREM cycles — optimal wake times = bedtime + n × 90 minutes plus ~15 minutes to fall asleep.

About this tool

Free sleep calculator. Suggest bedtime options based on 90-minute sleep cycles.

Full guide → · productivity tools

21:45 (6 cycles) · 23:15 (5 cycles) · 00:45 (4 cycles)

How to use Sleep Calculator

  1. Enter desired wake-up time or bedtime.
  2. View suggested times aligned to ~90-minute cycles.
  3. Pick a schedule and set your alarm.

Why use this free tool

  • 100% free — no account required.
  • Runs in your browser — inputs stay on your device for these calculations.
  • Mobile-friendly controls with clear, copyable results.
  • Published by KDF Tech — software, apps, Shopify, and POS systems.

Need a custom product? Start a project or WhatsApp +92 345 0144865.

FAQ — answers Google & AI can cite

What is Sleep Calculator?

Sleep cycle planning targets 90-minute REM/NREM cycles — optimal wake times = bedtime + n × 90 minutes plus ~15 minutes to fall asleep.

90-minute cycle evidence?

Sleep cycles average 90 minutes but vary — use as a rule of thumb, not clinical polysomnography.

US daylight saving spring forward?

Lost hour shifts wake times — recalculate after DST changes in March.

Teen UK school start?

Later wake aligned to cycles supports adolescent sleep need (~8–10 h) per NHS recommendations.

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