How long is one complete sleep cycle?

A complete sleep cycle commonly lasts around 80 to 100 minutes, although it can be shorter or longer. During each cycle, you move through stages of non-REM sleep before entering REM sleep. Cycle length also changes over the course of the night. Early cycles often contain more deep sleep and may differ in duration from later cycles, which usually include longer periods of REM sleep. This is why the popular 90-minute figure should be treated as an average rather than a fixed biological rule. Personal factors such as age, sleep deprivation, alcohol, medication, illness and stress can also affect sleep structure. Consumer calculators cannot identify the exact length of your individual cycles without measuring brain activity in a clinical sleep study.