Sleep Calculator
The Sleep Calculator suggests the best times to go to bed or wake up by aligning your alarm with complete 90-minute sleep cycles, so you wake feeling refreshed rather than groggy.
Why 90-minute cycles matter
Sleep runs in cycles of about 90 minutes, moving through light, deep, and REM stages. Waking in the middle of deep sleep leaves you groggy (sleep inertia), while waking at the end of a cycle feels much easier. The calculator counts backward or forward in 90-minute blocks to find those natural wake points.
How to use it
Tell it when you must wake up and it lists ideal bedtimes; tell it when you are going to bed and it lists good wake-up times. It also allows about 15 minutes to fall asleep. Most adults need 5–6 cycles (7.5–9 hours). Consistency - similar times every day - matters as much as the timing itself.
Frequently Asked Questions
How long is one sleep cycle?
About 90 minutes, cycling through light, deep, and REM sleep. Waking at the end of a cycle feels easier than waking mid-cycle.
How many sleep cycles do I need?
Most adults do best with five to six cycles per night, which is roughly 7.5 to 9 hours of sleep.
Why do I wake up groggy sometimes?
Waking during deep sleep causes sleep inertia. Aligning your alarm with the end of a cycle reduces that grogginess.
Does it account for time to fall asleep?
Yes. It typically adds about 15 minutes to fall asleep when suggesting bedtimes and wake times.
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