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Oneirox Lab · Free instrument · No login

Sleep Cycle Calculator

Sleep runs in ~90-minute ultradian blocks, alternating NREM and REM. Wake mid-cycle and you get sleep inertia — grogginess, not rest. Enter a wake time or bedtime and land on a cycle boundary instead.

90

minutes
per cycle

14

min average
sleep onset

Math only — no account, no data sent anywhere. Based on the ~90-minute ultradian rhythm (Kleitman) and average sleep-onset latency.

Each full cycle moves through light NREM, deep slow-wave sleep, and REM. Waking near a cycle boundary catches you in light sleep — the easiest state to surface from.

Science · not a lifehack

The ultradian rhythm, not a rule of thumb

Nathaniel Kleitman's basic rest-activity cycle (BRAC) and the classic Dement & Kleitman (1957) EEG studies established that human sleep alternates through NREM and REM in cycles averaging 90 minutes, four to six times a night. Cycle length is not perfectly fixed — it can range 70–110 minutes and shifts slightly across the night — so this calculator gives a small window of options rather than one rigid number.

Sleep inertia — the grogginess, slowed reaction time, and disorientation right after waking — is strongest when an alarm interrupts slow-wave (deep NREM) sleep. Waking during light NREM, near a cycle boundary, produces measurably less inertia. That is the entire mechanism this tool calculates for: not a lucky number, a boundary in your own ultradian rhythm.

This is a planning tool, not a Lab Search path. If a specific dream from one of these nights is still with you, open Lab Search for a mechanism-based interpretation — or add somatic detail first with the Sensory Dream Mapper.

Workflow

Three instruments, one lab

  1. 01

    Sleep Cycle Calculator

    Plan bedtime or wake time around 90-minute cycle boundaries — before you sleep.

  2. 02

    Sensory Mapper (optional)

    Map body sensations on waking — temperature, pressure, zones.

  3. 03

    Lab Search

    Describe the dream. Receive SIGNAL · BODY · MORNING — one flagship reading, limited per day.

Know your cycles.
Now explore the rest of the Lab.

Free · No login · 400+ body-signal profiles · 26 dream mechanisms

Open the Lab →

Why I built this — Vigen G.R. →