What is a sleep cycle calculator?

A sleep cycle calculator is a tool that suggests possible bedtimes or wake-up times based on estimated sleep-cycle lengths. Most calculators assume that sleep occurs in repeating cycles containing light sleep, deep sleep and REM sleep. You enter when you need to wake up or when you plan to go to bed, and the calculator estimates times that may place waking near the end of a cycle. It may also add time for falling asleep. The tool can be useful for planning, but it cannot monitor your actual sleep stages. Cycle length varies between people and throughout the night, so the results should be treated as estimates rather than precise medical advice.