Date & Time
Wake up at the end of a sleep cycle, not in the middle of one. Pick a wake-up time or a bedtime — the calculator does the 90-minute math.
Be in bed by these times — each one already includes 15 minutes to fall asleep.
Set your alarm for one of these — each includes 15 minutes to fall asleep after lights out.
A 20-minute power nap keeps you in light sleep, so you wake up clear instead of groggy. A 90-minute nap is one full sleep cycle — better when you have the time and need real recovery. Both alarms include the same 15 minutes to drift off, so a "20-minute nap" means about 35 minutes in bed.
You don't sleep at one steady depth. All night you loop through a sleep cycle — light sleep, deep sleep, and REM (dream) sleep — that takes about 90 minutes on average. Waking up in the middle of deep sleep is what causes that heavy, groggy feeling, even after a long night. Waking at the end of a cycle, when sleep is lightest, feels noticeably easier. A full night is usually 5 cycles (7½ hours) or 6 cycles (9 hours) of actual sleep.
This calculator works in whole 90-minute cycles and adds a 15-minute buffer — the average time it takes to fall asleep. To find a bedtime it counts backwards from your wake-up time; to find a wake-up time it counts forwards from when you get into bed. Six cycles is the full-restore option, five is the standard recommendation, and four (6 hours) is the short-night floor. Cycles vary a little from person to person, so if a suggested time still leaves you groggy, shift it by 10–15 minutes and see which suits you better.
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