Sleep Calculator
Find the best bedtime or wake-up time based on sleep cycles.
đ Runs entirely in your browser â nothing is uploaded.
âšī¸ Based on 90-minute sleep cycles plus ~15 minutes to fall asleep - a common rule of thumb, not a guarantee.
How Sleep Calculator works
How does the sleep calculator pick its suggested times?
It works in blocks of 90-minute sleep cycles, the commonly cited average length of one full cycle, offering 3, 4, 5, or 6 cycles as options. Given a wake-up time, it counts backward by 90 minutes per cycle and adds another 15 minutes to account for the time it typically takes to fall asleep; given a bedtime instead, it counts forward in 90-minute increments to suggest wake-up times.
When would I use this?
It's useful when you have a fixed wake-up time - an early flight or a work start, for instance - and want a bedtime that lines up with the end of a full cycle rather than the middle of one, which is the idea behind feeling less groggy on waking. It works in the other direction too, if you already know your bedtime and want to see good wake-up options.
Is waking up at a cycle boundary guaranteed to feel better?
Not guaranteed - 90 minutes is an average, and actual cycle length varies from person to person and night to night, so the suggested times are estimates rather than a precise schedule. This is a general rule of thumb, not medical advice; consistent sleep duration and timing matter more than hitting an exact cycle count.