Sleep runs in cycles of roughly 90 minutes. Most adults need 7–9 hours, which is about five to six cycles.
How to use the Sleep Calculator
- Wake-up hour (0–23)
- Wake-up minute
- Minutes to fall asleep
Results update as you type, and every field accepts the units shown in its menu.
How it works
Starting from your wake-up time, the calculator counts back whole cycles plus the time it takes to fall asleep.
Inputs explained
| Field | What to enter |
|---|---|
| Wake-up hour (0–23) | A number |
| Wake-up minute | A number |
| Minutes to fall asleep | A number |
What each result means
- Bedtime for 6 cycles (9 h) = [Wake time (hours)] – 9 – [Minutes to fall asleep]÷60
- Bedtime for 5 cycles (7.5 h) = [Wake time (hours)] – 7.5 – [Minutes to fall asleep]÷60
- Bedtime for 4 cycles (6 h) = [Wake time (hours)] – 6 – [Minutes to fall asleep]÷60
Health note: this calculator is for education and screening only and is not a diagnosis or treatment advice. Discuss your results with a qualified clinician.
Formula
Bedtime = wake time − (cycles × 90 min) − 15 minWorked example
Inputs — Wake-up hour (0–23): 7; Wake-up minute: 0; Minutes to fall asleep: 15.
Results — Bedtime for 6 cycles (9 h) = 21:45; Bedtime for 5 cycles (7.5 h) = 23:15; Bedtime for 4 cycles (6 h) = 00:45.
Frequently asked questions
Are all sleep cycles 90 minutes?
They range from about 70 to 120 minutes and change through the night.
How much sleep do adults need?
At least 7 hours, according to sleep medicine societies.
What formula does the Sleep Calculator use?
Bedtime = wake time − (cycles × 90 min) − 15 min.