Sleep Cycle Calculator
Pick a bedtime and see the wake-up times that land at the end of a 90-minute sleep cycle, after the minutes it takes you to fall asleep.
Wake at the end of a cycle, not the middle — these are the times.
How the sleep cycle calculator works
Sleep runs in cycles of light, deep and REM sleep lasting about 90 minutes each. Waking at the end of a cycle tends to feel easier than being pulled out of deep sleep midway. The calculator adds the time you take to fall asleep to your bedtime, then steps forward in cycles: six cycles is nine hours of sleep, five is 7½, four is six.
The 90-minute figure is an average — real cycles run 70 to 120 minutes and lengthen through the night — so treat the times as targets to test rather than a rule. Detailed mode lets you change the cycle length.
Formula: wake time = bedtime + minutes to fall asleep + cycles × cycle length
Worked examples
| Inputs | Wake after 6 cycles (about 9 h) | Note |
|---|---|---|
| Bed 22:30, asleep in 15 min | 07:45 | asleep 22:45, six cycles ends 07:45 |
| Bed 23:15, asleep in 10 min | 08:25 | a later night |
| Bed 21:00, asleep in 20 min | 06:20 | an early night |
FAQFrequently asked questions
How long is a sleep cycle?
About 90 minutes on average, ranging from roughly 70 to 120. The first cycles of the night carry more deep sleep, the later ones more REM.
How many cycles should I aim for?
Five or six — 7½ to 9 hours of sleep — is the range most adults do best on. Four cycles is a short night; three is an emergency.
Why add minutes to fall asleep?
Because the cycles start when you fall asleep, not when you lie down. Most people take 10–20 minutes; if it is regularly more than 30 or under 5, that is worth noting.
What if I want to work backwards from a wake time?
Subtract cycles: for a 06:30 alarm, count back 90-minute blocks plus your fall-asleep time — six cycles gives a 21:15 bedtime with 15 minutes to fall asleep.
Where these figures come from
- Mifflin MD et al., "A new predictive equation for resting energy expenditure in healthy individuals", Am J Clin Nutr 1990 — the BMR equation used here
- World Health Organization — Waist circumference and waist–hip ratio (2008 expert consultation) — waist-to-hip cut-offs
- Tanaka H, Monahan KD, Seals DR, "Age-predicted maximal heart rate revisited", J Am Coll Cardiol 2001 — 208 − 0.7 × age
- Nathan DM et al., "Translating the A1C assay into estimated average glucose values" (ADAG), Diabetes Care 2008 — eAG = 28.7 × A1c − 46.7
- Mosteller RD, "Simplified calculation of body-surface area", N Engl J Med 1987 — BSA = √(height × weight / 3600)
- Australian Department of Health and Aged Care — national health guidance
Last checked: September 2026. The equations are fixed by their published papers and do not change with tax years or regulations; the thresholds quoted in verdicts name the body that set them.