Sleep calculator
When to go to bed or wake up in full 90-minute sleep cycles, with CDC hours by age.
- ๐บ๐ธ US federal & state rules
- See sources
Bedtime to wake at 6:30 AM
10:45 PM or 9:15 PM
5 cycles (7 h 30 min of sleep) or 6 cycles (9 h), plus 15 min to fall asleep
- 5 cycles, 7 h 30 min
- 10:45 PM
- 6 cycles, 9 h
- 9:15 PM
- 4 cycles, 6 h (short)
- 12:15 AM
This is an example. Enter your numbers above and press the button to see your own result.
Go to bed at (by number of 90-minute cycles)
| 6 cycles, 9 h of sleep | 9:15 PM |
|---|---|
| 5 cycles, 7 h 30 min of sleep | 10:45 PM |
| 4 cycles, 6 h of sleep | 12:15 AM |
| 3 cycles, 4 h 30 min of sleep | 1:45 AM |
Recommended sleep by age (CDC)
| Newborn (0 to 3 months) | 14 to 17 hours |
|---|---|
| Infant (4 to 12 months) | 12 to 16 hours, naps included |
| Toddler (1 to 2 years) | 11 to 14 hours, naps included |
| Preschool (3 to 5 years) | 10 to 13 hours, naps included |
| 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 and older) | 7 to 8 hours |
- The NHLBI puts a sleep cycle at 80 to 100 minutes, with four to six cycles a night. This calculator uses 90 minutes, so treat the times as a starting point.
- The CDC recommends at least 7 hours a night for adults. Four cycles (6 hours) falls short of that.
- If you snore loudly, wake up gasping or feel sleepy during the day after 7 to 9 hours, talk to a doctor. This is an estimate for general information, not medical advice. Talk to a doctor or registered dietitian before a big change in diet or exercise, especially if you are pregnant or have a health condition.
Show the math
| Sleep for 5 cycles | 5 ร 90 min = 7 h 30 min |
|---|---|
| Time to fall asleep | 15 min |
| Bedtime | 6:30 AM - 7 h 45 min = 10:45 PM |
What to do next
How it works
The calculator counts back (or forward) in 90-minute sleep cycles and adds the time it takes you to fall asleep. Five cycles is 7 hours 30 minutes of sleep and six cycles is 9 hours, both inside the adult range.
Enter the time you need to wake up to get bedtimes, or the time you plan to go to bed to get wake times. Times work in 12-hour or 24-hour format.
Things to keep in mind
Cycle length differs between people and between cycles in the same night, so the exact minute matters less than getting enough total sleep on a regular schedule.
The age table follows the CDC. Ongoing trouble falling or staying asleep, loud snoring or daytime sleepiness are worth raising with a doctor. This page is not medical advice.
Sources
- CDC: About sleep, recommended hours of sleep by ageChecked 2026-10-19
- NHLBI: Sleep phases and stages (a cycle every 80 to 100 minutes, four to six a night)Checked 2026-10-19
Frequently asked questions
What time should I go to bed to wake up at 6:30 AM?
With 15 minutes to fall asleep, 5 cycles means bed at 10:45 PM and 6 cycles means 9:15 PM. Both end at the close of a cycle.
Why 90-minute sleep cycles?
Sleep moves through light, deep and REM stages in cycles of about 80 to 100 minutes, four to six times a night (NHLBI). Waking near the end of a cycle tends to feel less groggy than waking from deep sleep.
How many hours of sleep do adults need?
The CDC says adults 18 to 60 need 7 or more hours, 61 to 64 need 7 to 9 hours and 65 and older need 7 to 8 hours. Teens 13 to 17 need 8 to 10 hours.
Is 6 hours of sleep enough?
Six hours is 4 full cycles, but it is below the 7 hours the CDC recommends for adults. A short night now and then is fine; many short nights in a row add up.