Sleep Calculator
Sleep calculator that counts 90-minute cycles back from a wake-up time, or on from a bedtime or from now: 3 to 7 cycles, each with its hours of sleep. How it works
Use the Sleep Calculator
About the Sleep Calculator
To wake at 7:00 AM after whole 90-minute cycles, go to bed at 9:45 PM for 9 hours of sleep, 11:15 PM for 7.5 hours or 12:45 AM for 6 hours, allowing 15 minutes to fall asleep. This sleep calculator counts back from a wake-up time, or on from a bedtime you type or from now, and prints the hours of sleep beside every option. The CDC recommends 7 or more hours a night for adults aged 18 to 60, so the 6-hour and 4.5-hour options carry a note saying they fall short.
Bedtimes by wake-up time, allowing 15 minutes to fall asleep
| Wake-up time | 6 cycles (9 hours) | 5 cycles (7.5 hours) | 4 cycles (6 hours) |
|---|---|---|---|
| 5:00 AM | 7:45 PM | 9:15 PM | 10:45 PM |
| 5:30 AM | 8:15 PM | 9:45 PM | 11:15 PM |
| 6:00 AM | 8:45 PM | 10:15 PM | 11:45 PM |
| 6:30 AM | 9:15 PM | 10:45 PM | 12:15 AM |
| 7:00 AM | 9:45 PM | 11:15 PM | 12:45 AM |
| 7:30 AM | 10:15 PM | 11:45 PM | 1:15 AM |
| 8:00 AM | 10:45 PM | 12:15 AM | 1:45 AM |
| 8:30 AM | 11:15 PM | 12:45 AM | 2:15 AM |
| 9:00 AM | 11:45 PM | 1:15 AM | 2:45 AM |
Each bedtime is the wake-up time minus the cycles, minus 15 minutes. The calculator also lists a 3-cycle option, 4.5 hours of sleep, which is 90 minutes later than the 4-cycle bedtime, and a 7-cycle option (10.5 hours, 90 minutes earlier than 6 cycles) can be switched on. The 6-hour and 4.5-hour options are below the 7 or more hours the CDC recommends for adults.
Wake-up times by bedtime, allowing 15 minutes to fall asleep
| Lights out | 4 cycles (6 hours) | 5 cycles (7.5 hours) | 6 cycles (9 hours) |
|---|---|---|---|
| 9:00 PM | 3:15 AM | 4:45 AM | 6:15 AM |
| 9:30 PM | 3:45 AM | 5:15 AM | 6:45 AM |
| 10:00 PM | 4:15 AM | 5:45 AM | 7:15 AM |
| 10:30 PM | 4:45 AM | 6:15 AM | 7:45 AM |
| 11:00 PM | 5:15 AM | 6:45 AM | 8:15 AM |
| 11:30 PM | 5:45 AM | 7:15 AM | 8:45 AM |
| 12:00 AM | 6:15 AM | 7:45 AM | 9:15 AM |
| 12:30 AM | 6:45 AM | 8:15 AM | 9:45 AM |
| 1:00 AM | 7:15 AM | 8:45 AM | 10:15 AM |
What the “I go to bed at” mode shows for the bedtime in the first column, and what “Sleep now” shows when that is the current time: the time plus 15 minutes plus the cycles.
Recommended hours of sleep per day by age (CDC)
| Group | Age | Recommended sleep per day |
|---|---|---|
| Newborn | 0 to 3 months | 14 to 17 hours |
| Infant | 4 to 12 months | 12 to 16 hours (including naps) |
| Toddler | 1 to 2 years | 11 to 14 hours (including naps) |
| Preschool | 3 to 5 years | 10 to 13 hours (including naps) |
| School age | 6 to 12 years | 9 to 12 hours |
| Teen | 13 to 17 years | 8 to 10 hours |
| Adult | 18 to 60 years | 7 or more hours |
| Adult | 61 to 64 years | 7 to 9 hours |
| Adult | 65 years and older | 7 to 8 hours |
From the CDC’s “About Sleep” page, the same table the calculator shows under its results.
Methodology
Bedtime = wake-up time − cycles × 90 minutes − minutes to fall asleep. Wake time = bedtime (or the current time) + minutes to fall asleep + cycles × 90 minutes. Cycles run from 3 to 7, which are 4.5, 6, 7.5, 9 and 10.5 hours of sleep; 3 to 6 are shown until you change the selection. The minutes to fall asleep start at 15 and can be set from 0 to 120, and above 60 the page adds a note that every time shifts by that much. Options with less than 7 hours of sleep are marked with the CDC’s recommendation for adults.
How to use this tool
- Choose “Wake up at” and enter the time you have to be up, “I go to bed at” and enter a bedtime (Bed now fills in the current time), or “Sleep now” to count from the current time.
- Set the minutes you usually take to fall asleep, from 0 to 120, and pick which cycle counts to show, from 3 to 7.
- Read the options. Each shows the clock time, the cycles and the hours of sleep; in “Wake up at” mode each bedtime also carries its clock band (5 am to 10 pm, 10 pm to midnight, midnight to 2 am or 2 am to 5 am), which the Bedtime bands switch hides.
- In “I go to bed at” mode, open Cycle timeline for the start and end of each cycle. Copy link to these settings gives a link that reopens the page as you left it.
Frequently asked questions
- What time should I go to bed to wake up at 6 AM?
- 8:45 PM for 9 hours of sleep, 10:15 PM for 7.5 hours or 11:45 PM for 6 hours, if you take 15 minutes to fall asleep. Only the first two reach the 7 or more hours the CDC recommends for adults aged 18 to 60.
- If I go to bed at 11 PM, what time should I wake up?
- 5:15 AM after four cycles (6 hours of sleep), 6:45 AM after five (7.5 hours) or 8:15 AM after six (9 hours), allowing 15 minutes to fall asleep. Choose “I go to bed at” and enter 11:00 PM to see them, or press Bed now to start from the current time.
- How long is a sleep cycle?
- The calculator uses 90 minutes. The National Heart, Lung, and Blood Institute describes a cycle as starting over every 80 to 100 minutes, usually four to six times a night. If your cycles run 10 minutes longer or shorter than 90, the end of the sixth one is an hour away from the time shown.
- How many hours of sleep do I need?
- The CDC recommends 7 or more hours a day for adults aged 18 to 60, 7 to 9 hours at 61 to 64 and 7 to 8 hours from 65. Teens aged 13 to 17 are advised 8 to 10 hours and children aged 6 to 12 are advised 9 to 12.
- Will I feel rested if I wake at the end of a cycle?
- The calculator cannot tell you. It does arithmetic on an average cycle length and does not measure your sleep. The CDC states its recommendation in hours of sleep per day and describes quality sleep as uninterrupted and refreshing. Use the times to plan enough hours, not as a promise about the morning.
- What happens in each sleep cycle?
- Open Cycle timeline in “I go to bed at” mode. For an 11:00 PM bedtime and 15 minutes to fall asleep, cycle 1 runs from 11:15 PM to 12:45 AM and cycle 5 ends at 6:45 AM. Cycles 1 and 2 are labeled mostly deep NREM sleep with a short REM part, 3 and 4 less deep sleep with a longer REM part, and 5 on REM at its longest. That is the typical pattern across a night, deep sleep mostly early and REM mostly later (NHLBI), not a reading of your own sleep.
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