Sleep Cycle Calculator
Time your bedtime or wake-up around full 90-minute sleep cycles.
How We Calculate This
Sleep isn't one flat state — it moves through a repeating cycle of light sleep, deep sleep, and REM sleep that takes roughly 90 minutes to complete, with most adults getting through four to six full cycles a night. The National Institute of Neurological Disorders and Stroke (NINDS) describes this ultradian rhythm in its patient-education overview of sleep architecture.
Waking up in the middle of a cycle — mid-deep-sleep, for instance — tends to feel groggier than waking up right at the boundary between cycles, when sleep is naturally lighter. This calculator works backward (or forward) from your target wake-up time or bedtime in 90-minute increments, plus roughly 15 minutes to account for the time it typically takes to actually fall asleep, so the suggested times land on cycle boundaries rather than mid-cycle.
On sleep duration: the American Academy of Sleep Medicine and Sleep Research Society's joint consensus statement recommends adults get 7 or more hours of sleep per night for optimal health, which lines up with the 5-cycle (7.5 hour) and 6-cycle (9 hour) options here. Consistently sleeping less than 7 hours is associated with adverse health outcomes including weight gain, impaired immune function, and increased risk of cardiovascular disease.
Two things that reliably push against good sleep timing are caffeine and magnesium status — see our caffeine guide for how late-day caffeine quietly shortens total sleep time, and our magnesium guide for an honest look at the (thinner) evidence behind magnesium glycinate as a sleep aid.
Source: Watson NF, Badr MS, Belenky G, et al. Recommended Amount of Sleep for a Healthy Adult: A Joint Consensus Statement of the American Academy of Sleep Medicine and Sleep Research Society. Sleep. 2015;38(6):843–844.
Read the consensus statement on PubMed →