Crunch Sleep Calculator
Waking up groggy is often a timing problem, not a quantity problem. Sleep runs in 90-minute cycles, and waking at the end of one feels radically better than waking mid-cycle. Tell it when you must wake up — or when you plan to sleep — and it counts backwards or forwards in whole cycles.
How it works
A full sleep cycle — light sleep, deep sleep, dreaming — lasts about 90 minutes, and the average person takes about 14 minutes to fall asleep. So the math is: target time ∓ (cycles × 90 minutes) ∓ 14 minutes. Five cycles (7½ hours of sleep) suits most adults; six cycles (9 hours) is the full tank. The suggestions are ordered with the recommended 5–6 cycle options first.
Method & worked example
Method: Sleep runs in roughly 90-minute cycles, and falling asleep takes about 14 minutes on average. Bedtimes = wake time − (cycles × 90 minutes) − 14 minutes; wake times = bedtime + 14 minutes + (cycles × 90 minutes). Five or six cycles suit most adults.
Worked example: To wake at 6:30 AM: six cycles means lights out at 9:16 PM; five cycles — the sweet spot for most adults — means 10:46 PM. Going to bed at 11:00 PM instead, the matching wake times are 8:14 AM (six cycles) and 6:44 AM (five).
Frequently asked questions
What time should I go to bed if I wake up at 6:30 AM?
For six full cycles: lights out at 9:16 PM. For five cycles — the sweet spot for most adults — 10:46 PM. Four cycles means 12:16 AM and noticeably less deep sleep. Each option above includes the 14 minutes it takes to drift off.
I am going to bed at 11 PM — when should I set my alarm?
After five cycles: 6:44 AM. After six: 8:14 AM. Waking at, say, 7:00 instead slices into the middle of a cycle, which is why 7 can feel worse than 6:44 despite the extra minutes.
How many cycles do I need?
Most adults do best on 5–6 cycles (7½–9 hours of actual sleep). Teenagers need more; some adults genuinely thrive on the lower end. If you wake naturally before your alarm most days, you are probably landing at a cycle boundary already.
Why 14 minutes to fall asleep?
It is the widely used average sleep-onset latency for healthy adults. If you know you take longer — 30 minutes is common with screens in bed — shift every suggested time earlier by the difference.
📅 Counting sleeps until something big?
The Days Until Calculator counts the days, weeks and months to any date you name.