Sleep Calculator: Find Your Ideal Bedtime or Wake-Up Time
Based on natural 90-minute sleep cycles — wake up at the end of a cycle, not in the middle of one.
Calculate My Sleep Times
How This Calculator Works
90-minute cycles
Sleep moves through roughly 90-minute cycles of light, deep, and REM sleep. Waking mid-cycle (during deep sleep) is what causes that groggy, disoriented feeling.
Falling asleep takes time
Most people take about 15 minutes to actually fall asleep after getting into bed — this calculator accounts for that gap.
5–6 cycles is ideal
That's roughly 7.5–9 hours of sleep, aligned to cycle boundaries so you wake up at the lightest point of a cycle instead of the deepest.
Common Sleep Questions
Why can't I sleep even when I'm tired?
Common causes include screen exposure before bed, inconsistent sleep/wake times, caffeine late in the day, and stress. Timing your bedtime to align with a full sleep cycle (as this calculator does) can also make falling asleep and waking up feel easier.
How do I get more deep sleep?
Consistent sleep and wake times, avoiding late caffeine and alcohol, and keeping a cool, dark room all support deeper sleep. Waking at the end of a full cycle rather than mid-cycle also improves how rested you feel.
Is this sleep calculator accurate?
It's based on the well-established average 90-minute sleep cycle length, but individual cycle length varies somewhat from person to person. Treat the times shown as a strong starting estimate, not an exact science.
Can magnesium help me fall asleep faster?
Magnesium is commonly associated with supporting the body's relaxation response, which may help some people wind down before bed. It's not a sedative and works best as part of a consistent bedtime routine, not a one-time fix.