Ideal wake times using 90-minute cycles.
These calculators use established formulas (such as Mifflin-St Jeor for calorie needs or the Devine formula for ideal weight) to provide general estimates. They're built for a general population and don't account for individual medical conditions, medications, or circumstances. They aren't a substitute for advice from a doctor, registered dietitian, or other qualified healthcare provider — especially for anything related to pregnancy, chronic conditions, or medication dosing.
Sleep cycles average 90 minutes and include light, deep, and REM stages. Waking at end of a cycle feels more refreshing than mid-cycle.
This tool assumes ~14 min to fall asleep, then adds full 90-min cycles.
REM sleep, associated with dreaming and memory consolidation, becomes proportionally longer in later cycles of the night — which is part of why cutting sleep short tends to disproportionately reduce REM even if total hours look only slightly reduced.
Bedtime 23:00: ideal wakes ≈ 03:44 (3 cycles), 05:14 (4), 06:44 (5), 08:14 (6 = 9h).
Population average — individuals range 70–110. Experiment 10–20 min on either side of the suggestion.
Most adults do best on 7–9 hours (5–6 cycles). Consistency of bedtime often matters more than exact duration.
Many people report grogginess (sleep inertia) when woken from deep sleep stages versus lighter stages near a cycle boundary, which is the reasoning behind timing wake-ups to cycle length.