Sleep Calculator
Find the best bedtime based on 90-minute sleep cycles and your wake-up time.
Assumptions used in this calculation
- Fall-asleep buffer: Assumes about 14 minutes to fall asleep, the average found in sleep-onset research.
About this calculator
Waking up groggy often has less to do with total hours slept than with which sleep stage your alarm interrupted, being pulled out of deep sleep mid-cycle feels far worse than waking naturally between cycles, even with the same total sleep duration. This calculator works backward from your target wake-up time in increments of roughly 90 minutes, the average length of one full sleep cycle, and lists several bedtime options, each corresponding to a whole number of complete cycles before you need to wake up. It also builds in about a 14-minute buffer for the time it typically takes to actually fall asleep once you're in bed. Rather than just recommending a fixed "8 hours" and letting your alarm land wherever it lands within a cycle, this gives you a short list of bedtimes engineered to have your alarm go off between cycles, when waking tends to feel noticeably easier.
Worked example
Wake up at 7:00 AM
Result: Bedtime options: 9:46 PM, 11:16 PM, 12:46 AM, or 2:16 AM
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