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Plan bedtimes around sleep cycles — wake refreshed, not groggy.
Plan bedtimes around sleep cycles — wake refreshed, not groggy.
Enter values above and click Calculate — results will appear here with the formula explained.
Sleep moves through roughly 90-minute cycles of light, deep and REM stages. Waking mid-deep-sleep produces the leaden grogginess of sleep inertia even after adequate total rest; waking between cycles feels dramatically lighter.
Working backwards from your alarm, each candidate bedtime subtracts whole cycles plus realistic fall-asleep time — commonly underestimated at 15+ minutes. Three to six cycles span 4½ to 9 hours, letting you trade duration against schedule constraints consciously.
Plan bedtimes around sleep cycles — wake refreshed, not groggy. Formula: bedtime = wake − fallAsleep − cycles × 90 min. Example: A 07:00 alarm with 15-minute sleep onset: six full cycles means lights out by 21:45; five cycles allows 23:15; four desperate ones, 00:45.
Sleep moves through roughly 90-minute cycles of light, deep and REM stages. Waking mid-deep-sleep produces the leaden grogginess of sleep inertia even after adequate total rest; waking between cycles feels dramatically lighter.
Working backwards from your alarm, each candidate bedtime subtracts whole cycles plus realistic fall-asleep time — commonly underestimated at 15+ minutes. Three to six cycles span 4½ to 9 hours, letting you trade duration against schedule constraints consciously.
A 07:00 alarm with 15-minute sleep onset: six full cycles means lights out by 21:45; five cycles allows 23:15; four desperate ones, 00:45.
Formulas are standard public references (see our methodology). External standards are cited in the text where they apply.
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