Sleep Cycle Calculator
Enter the time you need to wake up, or the time you plan to go to bed. The calculator lists times that fall at the end of complete sleep cycles.
Result
Go to bed at one of these times
| Bedtime | Cycles | Sleep |
|---|---|---|
| 9:45 PM | 6 | 9 h 00 min |
| 11:15 PM | 5 | 7 h 30 min |
| 12:45 AM | 4 | 6 h 00 min |
| 2:15 AM | 3 | 4 h 30 min |
Sleep cycles average about 90 minutes but vary between people and through the night. Most adults need 7 to 9 hours of sleep. This is general information and not medical advice.
Formula
- Bedtime = wake time − (cycles × cycle length) − time to fall asleep
- Wake time = bedtime + time to fall asleep + (cycles × cycle length)
- 5 cycles = 7.5 hours and 6 cycles = 9 hours at 90 minutes each
How the Sleep Cycle Calculator works
Sleep runs in cycles of light sleep, deep sleep and REM sleep, each lasting roughly 90 minutes. Waking during deep sleep leaves you groggy, an effect called sleep inertia. Waking near the end of a cycle feels easier.
The calculator counts back from your wake time in whole cycles and allows time to fall asleep, which averages 10 to 20 minutes for healthy adults.
Worked example
To wake at 7:00 AM after five cycles: 5 × 90 minutes = 7 hours 30 minutes of sleep, plus 15 minutes to fall asleep. Go to bed at 11:15 PM. For six cycles, go to bed at 9:45 PM.
Frequently asked questions
How many sleep cycles do I need?
Most adults do best with five or six cycles a night, which is 7.5 to 9 hours.
How long should a nap be?
Either about 20 minutes, to stay in light sleep, or a full cycle of about 90 minutes. Naps in between tend to end in deep sleep.
Related calculators
- Time Calculator: Add and Subtract TimeAdd and subtract hours, minutes and seconds. Get the total as a duration, in decimal hours, and in minutes and seconds.
- Time Duration CalculatorCalculate the time between two dates and times in days, hours and minutes. Find how many hours passed between two clock times.
- Heart Rate Zone CalculatorCalculate your maximum heart rate and five training zones from your age, with optional Karvonen zones using resting heart rate.
- Gear Ratio CalculatorCalculate gear ratio from tooth counts with output speed and torque, or find vehicle speed from engine RPM, axle ratio and tire diameter.
- Engine Displacement CalculatorCalculate engine displacement in cc, liters and cubic inches from bore, stroke and number of cylinders.
- Power to Weight Ratio CalculatorCalculate power to weight ratio in hp per pound, hp per ton, watts per kilogram and pounds per horsepower for cars, motorcycles and cyclists.
- Tire Size CalculatorCalculate tire diameter, sidewall height, circumference and revolutions per mile from a metric tire size, and compare two sizes with the speedometer difference.
- Animal Gestation CalculatorCalculate the due date for cows, horses, goats, sheep, pigs, dogs, cats and rabbits from the breeding date, with the normal range.
- ERA CalculatorCalculate earned run average (ERA) and WHIP for baseball and softball pitchers from earned runs, innings pitched, hits and walks.
- Batting Average CalculatorCalculate batting average, on-base percentage, slugging percentage and OPS for baseball and softball from at-bats, hits, walks and extra-base hits.
- Winning Percentage CalculatorCalculate winning percentage from wins, losses and ties, and see how many more wins are needed to reach a target percentage.
Related unit converters
Calculations run in your browser and nothing you enter is sent to a server. Results are provided for general information. Check critical figures independently before relying on them.