SnapCalc

Sleep Cycle & Bedtime Calculator

Calculate the best bedtime or wake-up time based on 90-minute sleep cycles to wake up feeling refreshed.

Enter as HHMM e.g. 630 = 6:30am, 2230 = 10:30pm

Average is 10–20 minutes

How to Use

  • Bedtime finder: Enter your required wake-up time to see the best times to go to sleep
  • Wake-up finder: Enter your planned bedtime to see the best times to set your alarm

    • Always aim to complete full 90-minute cycles. Waking mid-cycle causes sleep inertia — that groggy feeling.

    Formula

    Bedtime = Wake Time − Fall Asleep Time − (Cycles × 90 minutes)

    Frequently Asked Questions

    Why are sleep cycles 90 minutes?

    Each sleep cycle includes light sleep, deep sleep, and REM (dream) sleep. Cycles average 90 minutes, though early cycles have more deep sleep and later cycles more REM.

    How many sleep cycles do I need?

    Most adults need 5–6 cycles (7.5–9 hours). Less than 4 cycles (6 hours) consistently impairs cognition, immune function, and emotional regulation.

    Why do I feel worse after sleeping longer?

    Waking mid-cycle causes sleep inertia — grogginess that can last 1–2 hours. Timing your alarm to the end of a cycle (even if it means less total sleep) often feels better.

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