When should you go to bed?

Sleep cycles average 90 minutes across most adults. Some people run shorter (70–80 min) and some run longer (100–110 min), but 90 is the canonical figure researchers cite. We use it because the alternative — measuring your actual cycle length — requires a sleep lab.

That is normal. Brief awakenings between cycles are expected and most people fall back asleep without remembering them. The calculator assumes a continuous night; if your wake-ups last more than a few minutes, see a sleep clinician.

For most adults, yes. The 7.5-hour figure aligns with the National Sleep Foundation's recommended adult range (7–9 hours). Six cycles (9 hours) is fine if you naturally need more sleep; four (6 hours) is short-term acceptable but not a sustainable pattern.

Adolescent sleep need is roughly 30 percent higher than adult need due to brain development and hormonal shifts. Teens average 8–10 hours of sleep on a normal schedule; six full cycles (9 hours) hits the middle of that range.

The alternatives show how an extra cycle (more sleep) or one fewer cycle (less sleep, later bedtime) compares. If you cannot hit the recommended bedtime, the earlier option is the safer trade-off. The later option is a fallback for nights when sleep starts late.

The 90-minute cycle figure is from Carskadon and Dement's chapter in the Principles and Practice of Sleep Medicine (2017). Cycle structure varies by age and individual; the heuristic in this calculator is a generalisation, not a diagnosis.