Sleep Cycle Calculator
How it works
Each option here is a whole number of ~90-minute sleep cycles, plus a fixed ~14 minutes budgeted for falling asleep. Going the "bedtime" direction, that is subtracted from the wake-up time; going the "wake time" direction, it is added to the bedtime — either way wrapping past midnight correctly when the math crosses into the next (or previous) day.
The three options shown are 4, 5 and 6 cycles — 6, 7.5 and 9 hours of sleep. All three end between cycles rather than partway through one, which is the actual target here: waking up mid-cycle, during deeper sleep, is what tends to leave someone groggy, more than the raw number of hours does.
Frequently asked questions
Why 90 minutes?
That is a commonly used average length for one full sleep cycle. It varies from person to person and night to night, so it is a rule of thumb this calculator is built on, not a guarantee of your own exact timing.
Why does it add 14 minutes?
That is a typical amount of time to fall asleep after getting into bed. It is added to (or subtracted from) the cycle math so the bedtime or wake time shown accounts for lying awake first, not just the sleep itself.
Why show several options instead of one ideal time?
The goal is waking up between cycles rather than in the middle of one, and several cycle counts land on that goal — not just whichever is closest to 8 hours. Total hours slept is one useful number, but which option feels best can still depend on how many cycles suit you.