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Sleep calculator

Wake up refreshed by timing 90-minute sleep cycles. Pick a wake-up time to get ideal bedtimes, or enter your bedtime to find the best times to wake.

Your schedule

Results update instantly.

Most people need about 15 minutes to fall asleep after getting into bed.
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Set your time on the left for ideal bedtimes.

General information only: this is a scheduling tool based on average 90-minute sleep cycles, not medical advice.
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The 90-minute sleep cycle

Each night your brain moves through cycles of about 90 minutes: light sleep, deep sleep, then REM (dream) sleep. Waking at the end of a cycle, during light sleep, feels natural. Being ripped out of deep sleep mid-cycle is what causes that heavy, groggy feeling, even after 8 hours in bed.

That is why the math is simple: take your wake time (or bedtime), add the minutes you need to fall asleep, then step in 90-minute chunks. Most adults feel best on 5 to 6 cycles, which is 7.5 to 9 hours of actual sleep.

How to use the results

  • Pick the highlighted option (7.5 or 9 hours) when you can; both land in the recommended range.
  • Short on time? 6 hours (4 cycles) beats 7 hours, because 7 lands you mid-cycle.
  • Keep it consistent: going to bed and waking at the same times trains your body to complete cycles cleanly.
  • Naps: one cycle (90 minutes) or a 20-minute power nap that ends before deep sleep.

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Sleep calculator FAQs

What is a sleep cycle?
A sleep cycle is the roughly 90-minute journey from light sleep through deep sleep to REM (dream) sleep. Waking up at the end of a cycle, during light sleep, feels much easier than being woken from deep sleep in the middle of one.
How many hours of sleep do adults need?
Most adults do best on 7 to 9 hours, which is 5 to 6 full 90-minute cycles. That is why the calculator highlights the 5-cycle (7.5 hours) and 6-cycle (9 hours) options.
Why does the calculator add time to fall asleep?
Most people need about 15 minutes to fall asleep after getting into bed. The calculator subtracts (or adds) that buffer so the 90-minute cycles are counted from when you actually fall asleep, not from when your head hits the pillow.
I wake up groggy even after 8 hours. Why?
You may be waking mid-cycle. Eight hours is about 5.3 cycles, so the alarm can land in deep sleep. Try shifting your bedtime or alarm by 30 to 90 minutes so you wake at a cycle boundary instead.
Is this medical advice?
No. This is a general scheduling tool based on average 90-minute sleep cycles. It is not medical advice. If you snore heavily, gasp, or feel exhausted despite enough sleep, talk to a doctor about a possible sleep disorder.
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