Sleep Calculator
Find the best bedtime or wake-up time based on 90-minute sleep cycles.
About the Sleep Calculator
Sleep happens in cycles of roughly 90 minutes, and waking up in the middle of a cycle tends to feel groggier than waking up between cycles. This calculator suggests bedtimes or wake times that align with complete 90-minute cycles, based on a target wake-up or bedtime.
How It Works
The calculator adds your typical time to fall asleep to the target time, then counts backward or forward in 90-minute increments (representing 4, 5, and 6 full sleep cycles) to suggest several bedtime or wake-time options that align with completing whole sleep cycles.
Suggested times = Target Time ± (Cycles × 90 minutes), for 4, 5, and 6 cycles, adjusted for time to fall asleep.
Example
Scenario: Needing to wake up at a specific time, wanting to know good bedtime options.
Result: Several suggested bedtimes, each corresponding to 4, 5, or 6 complete 90-minute sleep cycles before the wake time.
Assumptions & Limitations
- Assumes an average sleep cycle length of 90 minutes, which is a commonly cited estimate though actual cycle length varies somewhat by individual and by night.
- Includes your typical time to fall asleep in the calculation before counting cycles.
- Sleep cycle length is not perfectly fixed at 90 minutes for everyone — treat the suggested times as a helpful guide rather than an exact science.