How to use this calculator
- Enter or choose i know.
- Enter or choose time.
- Enter or choose time to fall asleep.
- Enter or choose cycle length.
- The 5 cycles (7.5 h asleep) updates as you type. Use Copy result or Share to keep it.
Method
Bedtime = Wake-up time − Time to fall asleep − Cycles × Cycle length; Wake-up time = Bedtime + Time to fall asleep + Cycles × Cycle length
- Cycle length
- about 90 minutes on average
- Time to fall asleep
- typically 10–20 minutes
Worked example
- Five cycles = 5 × 90 = 450 minutes = 7 h 30 min of sleep.
- 07:00 − 7 h 30 min − 15 min to fall asleep = 23:15.
- Six cycles (9 h) moves bedtime 90 minutes earlier, to 21:45.
To wake at 7:00 am after five full cycles, be in bed by about 11:15 pm.
What the result means
The American Academy of Sleep Medicine recommends that adults get 7 or more hours a night, so five or six cycles is the usual target. Four cycles (6 hours) is short for most adults.
Assumptions and limits
- Every cycle is the same length. Real cycles vary from about 70 to 120 minutes and change through the night.
- You fall asleep in the time entered.
- A cycle-based time is a rough guide, not a guarantee of waking at the end of a cycle.
- This tool does not assess sleep disorders. Persistent tiredness despite enough sleep is worth discussing with a doctor.
Questions
How long is a sleep cycle?
About 90 minutes on average. Early cycles are often shorter and later ones longer, and a typical night has four to six.
How much sleep do adults need?
The American Academy of Sleep Medicine recommends 7 or more hours per night for adults.
Sources
Please note: This is a general screening estimate for adults, not medical advice or a diagnosis. Talk to a qualified health professional about your health.