Sleep Calculator
This sleep calculator works out bedtimes for a chosen wake-up time, or wake-up times for a chosen bedtime, in whole sleep cycles. It adds the time you usually need to fall asleep and suggests the shortest option that still meets the recommended hours of sleep for your age group. The cycle length is an average, so treat the times as a starting point, not a precise schedule.
Updated
Results
- Sleep cycles
- SleepNot counting time to fall asleep
- Time in bed
- All options (6 · 5 · 4 · 3 cycles)
- Recommended minimumCDC, for your age group
- Recommended maximumShown for age groups with an upper limit
| Cycles | Time | Sleep | Time in bed | Compared with recommendation |
|---|
Results are estimates. See the methodology below.
How to use the calculator
- Choose a mode: I want to wake up at (to get bedtimes) or I’m going to bed at (to get wake-up times).
- Enter the time.
- Enter how many minutes it usually takes you to fall asleep. The default is 15 minutes, which is only a starting value; use your own.
- Pick your age group.
- Optionally, change the cycle length in the advanced options (default 90 minutes).
You get a suggested time plus the full list for 6, 5, 4 and 3 cycles, with the sleep and time in bed for each and how it compares with the recommendation. The recommended maximum is shown only for age groups that have one.
How it is calculated
Bedtime = wake-up time − (time to fall asleep + cycles × cycle length)
Wake-up time = bedtime + time to fall asleep + cycles × cycle length
The calculator tries 6, 5, 4 and 3 cycles. The suggestion is the option with the fewest cycles whose sleep, not counting the time to fall asleep, reaches the minimum for your age group. If none does, it suggests 6 cycles.
Recommended sleep by age (CDC)
| Age | Recommended per day |
|---|---|
| Teens 13–17 | 8–10 hours |
| Adults 18–60 | 7 or more hours |
| Adults 61–64 | 7–9 hours |
| Adults 65 and older | 7–8 hours |
The CDC draws these from the American Academy of Sleep Medicine (teens; adults 18–60, with the Sleep Research Society) and the National Sleep Foundation (adults 61 and older).
About the 90-minute cycle
The Sleep Foundation says cycles last about 90 minutes on average, with four to six in a typical night. The first is often 70 to 100 minutes and later ones 90 to 120 minutes, and they vary from person to person and night to night. The calculator cannot know your actual cycles.
Examples
Adult waking at 7:00 AM
Bedtimes: 9:45 PM (6 cycles), 11:15 PM (5 cycles), 12:45 AM (4 cycles) and 2:15 AM (3 cycles). The suggestion is 11:15 PM: 7 h 30 min of sleep and 7 h 45 min in bed, which meets the 7-hour minimum. The 4- and 3-cycle options fall below it.
Adult going to bed at 10:30 PM
Wake-up times: 7:45 AM, 6:15 AM, 4:45 AM and 3:15 AM. The suggestion is 6:15 AM, again 5 cycles.
Teen waking at 6:30 AM
Five cycles give only 7 h 30 min, under the 8-hour minimum for teens, so the suggestion becomes 9:15 PM (6 cycles, 9 h of sleep). For an adult 65 or older with the same wake-up time, the suggestion is 10:45 PM, and the 6-cycle option is above the 7–8 hour range.
How to read the result
Waking between cycles rather than in the middle of one is a popular idea for feeling less groggy, but this calculator does not show that it works for you. Getting enough total sleep matters more than hitting an exact minute. Treat the suggested time as a target and adjust after a week or two based on how rested you feel.
The calculator does not account for naps, shift work, sleep debt or whether you are naturally an early or late sleeper. It is not for children under 13. If you regularly have trouble sleeping or feel unusually tired during the day, talk to a doctor.
Frequently asked questions
How long is a sleep cycle?
About 90 minutes on average, but the first cycle is often 70 to 100 minutes and later cycles 90 to 120 minutes. NINDS notes that REM sleep first occurs about 90 minutes after falling asleep.
How much sleep do adults need?
The CDC lists 7 or more hours for adults 18–60, 7–9 hours for ages 61–64 and 7–8 hours for 65 and older. Teens 13–17 need 8–10 hours.
What time should I go to bed to wake up at 7 AM?
For an adult who takes 15 minutes to fall asleep, 11:15 PM gives five 90-minute cycles, or 7 h 30 min of sleep. 9:45 PM gives six cycles, or 9 hours.
Why does the calculator add time to fall asleep?
Cycles only start once you are asleep. Without that buffer, every bedtime would be too late. Enter what is realistic for you; the default of 15 minutes is a placeholder, not a medical norm.
Should I change the cycle length?
Only if you have a reason to. If you consistently wake up naturally a little before or after the suggested times, try a slightly shorter or longer cycle in the advanced options.
What else helps me sleep better?
The CDC suggests going to bed and getting up at the same time every day, keeping your bedroom quiet, relaxing and cool, turning off electronic devices at least 30 minutes before bed, avoiding caffeine in the afternoon or evening, and avoiding large meals and alcohol before bedtime.
Sources
This calculator gives general estimates based on average sleep cycles and is not medical advice. If you have ongoing sleep problems, talk to your doctor.