Sleep Calculator
Find the best time to go to bed or wake up so you finish whole 90-minute sleep cycles.
Cycle length varies from person to person (roughly 90–120 minutes) and through the night, so treat these times as a guide. This is not medical advice — talk to a doctor if you often feel unrefreshed after a full night’s sleep.
About this tool
Choose whether you know your wake-up time or your bedtime and enter it. The calculator allows about 15 minutes to fall asleep and counts back or forward in 90-minute sleep cycles, suggesting times for 6, 5, 4 and 3 full cycles so you are more likely to wake at the end of a cycle rather than in the middle of one.
Frequently asked questions
It assumes it takes about 15 minutes to fall asleep and that each sleep cycle lasts about 90 minutes. To wake at 7:00 AM after 5 cycles, count back 5 × 90 = 450 minutes plus 15 minutes: go to bed at 11:15 PM.
An adult sleep cycle lasts roughly 90 to 120 minutes, and you go through four to six cycles a night. The calculator uses 90 minutes, the figure most commonly quoted.
Most adults need 7 to 9 hours a night. Five cycles give 7.5 hours of sleep and six cycles give 9 hours, so those are the first two suggestions; 4 cycles (6 hours) is better than waking mid-cycle but is short for most people.
Waking from deep sleep in the middle of a cycle can leave you feeling groggy (sleep inertia). Timing your alarm to the end of a cycle may help, but if you regularly feel unrefreshed after 7–9 hours, talk to a doctor.
Related tools
BMI CalculatorWork out your BMI and see where it falls in the healthy range.Running Pace CalculatorCalculate your running pace per km and per mile, and your speed, from distance and finish time.Calories Burned Walking CalculatorEstimate how many calories you burn walking from your weight, walking speed and time.