SLEEP
CALCULATOR
Calculate your ideal bedtime and wake time based on 90-minute sleep cycles.
What This Calculator Does
The Sleep Calculator finds your optimal bedtime and wake-up times based on 90-minute sleep cycles and the average 14-minute sleep onset time. Waking at the end of a cycle (rather than mid-cycle) dramatically reduces grogginess.
The Formula Explained
Sleep cycles last ~90 minutes. Adults need 5–6 complete cycles (7.5–9 hours). Add 14 minutes to fall asleep. Example: wake at 7:00am → work back: 6 cycles = 9h + 14min = bedtime 9:46pm. 5 cycles = 7.5h + 14min = bedtime 11:16pm.
What Your Result Means
Your recommended bedtime and wake times are a starting point, not a rigid rule — treat them as a target to test and adjust based on how you feel. Sleep duration can also influence weight management: in one small controlled study, adults restricted to 5.5 hours of sleep lost significantly less body fat during a calorie deficit than those who slept 8.5 hours (Nedeltcheva et al., 2010). Short sleep has also been linked to higher ghrelin (a hunger-signaling hormone) and lower leptin (a satiety-signaling hormone) in some studies, which may make appetite harder to manage. These are associations from limited research, not guarantees for every individual — consult a healthcare provider about how sleep fits into your overall health plan.
Calorie Calculator to optimise nutrition alongside sleep · Read: How Sleep Affects Weight Loss
The 90-Minute Sleep Cycle
Human sleep follows cycles of approximately 90 minutes, progressing through light sleep, deep sleep (slow-wave sleep), and REM sleep. Waking at the end of a complete cycle — rather than mid-cycle — dramatically reduces morning grogginess (sleep inertia). This calculator accounts for the average 14-minute sleep onset time, so the recommended bedtimes will have you falling asleep at the start of a cycle.
How Much Sleep Do You Need?
The National Sleep Foundation recommends 7–9 hours for adults aged 18–64. Chronic sleep deprivation (under 7 hours) is associated with increased obesity risk, impaired glucose metabolism, elevated cortisol, reduced testosterone, impaired immune function, and increased all-cause mortality risk.