Sleep Calculator
Find the best time to go to bed or wake up based on 90-minute sleep cycles.
How to use the Sleep Calculator
- 1Choose whether you know your wake-up time, your bedtime, or want to sleep now.
- 2Adjust how long you usually need to fall asleep.
- 3Pick one of the suggested times that ends on a full sleep cycle.
About Sleep Calculator
The Sleep Calculator suggests bedtimes and wake-up times that line up with full sleep cycles. Enter the time you need to get up and it tells you when to go to bed; enter a bedtime, or choose Sleep now, and it shows when to set the alarm. Each option lists the number of cycles and the total sleep it gives, and the options with 7 to 9 hours of sleep are marked as recommended.
Sleep runs in cycles of light, deep and REM sleep that last about 90 minutes on average. The calculator adds the time it takes you to fall asleep, 15 minutes by default and adjustable from 0 to 60, and lets you set your own cycle length between 70 and 120 minutes if you know it from a sleep tracker. Times are shown in a 12-hour or 24-hour clock, and the list can be copied.
It helps anyone who wakes up groggy despite enough hours in bed, shift workers planning sleep at unusual times, students before an exam and travelers adjusting to a new schedule. Regular sleep also matters for training: see the Heart Rate Zone Calculator for planning easy and hard days.
Frequently asked questions
How long is a sleep cycle?
A full cycle through light sleep, deep sleep and REM sleep lasts about 90 minutes on average, though it ranges from roughly 70 to 120 minutes between people and over the night.
What time should I go to bed to wake up at 7 AM?
With 90-minute cycles and 15 minutes to fall asleep, go to bed at 9:45 PM for six cycles (9 hours) or 11:15 PM for five cycles (7.5 hours).
Why do I feel tired after a full night's sleep?
Waking up from deep sleep causes sleep inertia, a groggy feeling that can last up to an hour. Waking at the end of a cycle, in light sleep, usually feels easier.
How much sleep do adults need?
Health organizations recommend 7 to 9 hours for adults, which is about five or six 90-minute cycles. Teenagers need 8 to 10 hours.
More in Health & Fitness
Work out running pace, finish time or distance, with splits and speed for any race.
Estimate your due date, current pregnancy week, trimester and key milestones.
Estimate ovulation day, fertile window and next periods for the coming cycles.