Sleep Calculator
Find the best bedtime or wake time based on 90-minute sleep cycles.
Sleep happens in roughly 90-minute cycles, and waking up mid-cycle (rather than between cycles) tends to feel groggier — this calculates bedtime or wake time options aligned to full cycles.
Why cycle-aligned timing can feel better
Waking during deep sleep (mid-cycle) commonly produces grogginess, even after a full night's sleep — timing your alarm for the end of a cycle, rather than a fixed number of hours, is a commonly cited strategy for feeling more rested.
Frequently asked questions
How many sleep cycles do I need?
Most adults need 5-6 full 90-minute cycles per night — roughly 7.5 to 9 hours — though individual needs vary.
Is the 90-minute cycle length exact for everyone?
It's an average — actual cycle length varies somewhat by individual and even by night, so treat this as a helpful estimate rather than a precise science.