Sleep Cycle Calculator: Bedtimes and Wake-Up Times
This sleep cycle calculator works out when to go to bed or when to wake up, using the common model of sleep in 90-minute cycles. Enter your wake-up time and it lists four bedtimes, or choose Sleep now and it lists four wake-up times counted from the current clock time. There is no button to press: the list updates as you change anything. It is a timing calculator, not a medical tool, and the sums run in your browser.
How to find what time to go to bed
- Keep Wake up at selected. It is the default.
- Set the Wake-up time field to the time your alarm will go off. It starts at 07:00.
- Read the list headed Go to bed at one of these times. The earliest bedtime comes first, and it is the one with the most sleep.
- Check the line under the list. It says the bedtimes already include the minutes you need to fall asleep, 15 by default.
11:15 PM: 5 cycles · 7 h 30 min, Optimal
12:45 AM: 4 cycles · 6 h, Suboptimal
2:15 AM: 3 cycles · 4 h 30 min, Suboptimal
Times are written in the 12-hour clock style, such as 9:45 PM.
How to find what time to wake up if you sleep now
Choose Sleep now. The time picker disappears because the calculator uses the current time, and the heading changes to Wake up at one of these times. The note under the list reads, for example, It is 11:00 PM now. Times assume you fall asleep 15 min from now. The clock refreshes about every 15 seconds while this mode is open, so leave it open and the times stay current.
5:15 AM: 4 cycles · 6 h, Suboptimal
6:45 AM: 5 cycles · 7 h 30 min, Optimal
8:15 AM: 6 cycles · 9 h, Optimal
This is the only mode that starts from a bedtime, and the bedtime is always the current time. To plan from a different bedtime, work from the wake-up end: choose Wake up at and see which listed bedtime is closest to yours.
What Optimal and Suboptimal mean
Each row shows the time, the number of cycles with the sleep length (for example 5 cycles · 7 h 30 min), and a badge. Optimal marks 5 and 6 cycles, which are 7 h 30 min and 9 h at the default length. Suboptimal marks 3 and 4 cycles, 4 h 30 min and 6 h. The badge only reflects the number of cycles. It does not measure your sleep or judge your health, and the sleep length shown does not include the time spent falling asleep.
Settings: time to fall asleep and cycle length
Open Settings to change the two numbers behind the results. Values outside the allowed range are moved to the nearest limit.
| Field | Range | Default | What it changes |
|---|---|---|---|
| Time to fall asleep (minutes) | 0 to 120 | 15 | Moves every bedtime earlier, or every wake-up time later, by this many minutes. |
| Cycle length (minutes) | 60 to 120 | 90 | Sets how long each cycle lasts, so the sleep length on each row changes. |
For example, a wake-up time of 07:00 with a 30-minute fall-asleep time and 100-minute cycles gives 5 cycles · 8 h 20 min and a 10:10 PM bedtime.
How the times are calculated
- Wake up at: bedtime = wake-up time − (cycles × cycle length) − time to fall asleep, for 6, 5, 4 and 3 cycles.
- Sleep now: wake-up time = current time + time to fall asleep + (cycles × cycle length), for 3, 4, 5 and 6 cycles.
Times wrap past midnight, so a bedtime of 2:15 AM for a 7:00 AM alarm is the same night’s sleep. Everything is computed in your browser from the clock on your device, and nothing you enter is sent or stored.
What this calculator does not do
- It does not detect your sleep stages or track your sleep. The 90-minute cycle is a model, and sleep cycles vary from person to person.
- It has no age, gender or baby settings. The only inputs are the wake-up time, the two Settings fields and the mode.
- It does not offer nap lengths. The list covers 3 to 6 cycles only.
- It does not give medical advice or say how much sleep you should get.
To count down to an alarm, a countdown timer does that job.
Frequently asked questions
How do I use a sleep cycle calculator to find when to wake up?
Choose Sleep now, and the calculator adds the time you need to fall asleep (15 minutes by default) to the current time, then counts forward in 90-minute steps. The list under Wake up at one of these times shows four wake-up times, for 3, 4, 5 and 6 cycles, earliest first. Already know your alarm time? Choose Wake up at instead and read the bedtimes.
What time should I go to bed to wake up at 7am?
With the default settings (15 minutes to fall asleep, 90-minute cycles), a 7:00 AM wake-up gives four bedtimes: 9:45 PM for 6 cycles, 11:15 PM for 5 cycles, 12:45 AM for 4 cycles and 2:15 AM for 3 cycles. Set the Wake-up time field to 07:00, which is already the starting value, and the list shows them. Times appear in the 12-hour style, such as 9:45 PM.
What time should I wake up if I go to bed now?
Choose Sleep now. The calculator reads your device clock and lists four wake-up times for 3 to 6 cycles. If it is 11:00 PM and you need 15 minutes to fall asleep, the times are 3:45 AM, 5:15 AM, 6:45 AM and 8:15 AM. The note under the list shows the clock time it used and refreshes about every 15 seconds.
How do you calculate sleep cycles?
Multiply the cycle length by the number of cycles, then add the time it takes to fall asleep. For bedtimes: wake-up time minus cycles times cycle length minus time to fall asleep. For wake-up times: now plus time to fall asleep plus cycles times cycle length. With 90-minute cycles, 5 cycles is 450 minutes, or 7 h 30 min of sleep. The calculator does this for 3, 4, 5 and 6 cycles.
How many hours is 5 sleep cycles?
At the default 90 minutes per cycle, 5 sleep cycles is 7 hours 30 minutes, and 6 cycles is 9 hours. 4 cycles is 6 hours and 3 cycles is 4 hours 30 minutes. Each row shows this as, for example, 5 cycles · 7 h 30 min. The figure counts sleep only, not the minutes spent falling asleep. If you change Cycle length (minutes), every figure changes with it.
Is the 90 minute sleep cycle real?
A cycle of about 90 minutes is the commonly quoted average, but sleep cycles vary from person to person and from night to night, so 90 minutes is an average, not a rule. That is why the Settings section lets you set Cycle length (minutes) anywhere from 60 to 120. Treat the result as a timing estimate, not a measurement of your own sleep.
How long does it take to fall asleep?
It differs between people and between nights. The calculator assumes 15 minutes and lets you change it: open Settings, then enter a value from 0 to 120 in Time to fall asleep (minutes). The bedtimes and wake-up times shift by exactly that amount. If you are unsure, note roughly how long it takes you for a few nights and use that number.
Is there a sleep cycle calculator for naps?
Not as a separate mode. The list always covers 3 to 6 cycles, so the shortest result is 4 h 30 min at 90-minute cycles, or 3 h with a 60-minute cycle length. That is a sleep period, not a short nap. For a short nap, a plain countdown is the better fit.
Does the sleep cycle calculator change with age?
No. There is no age or gender field, and the same arithmetic is used for everyone. If you want to test a different rhythm, change Cycle length (minutes) in Settings, which accepts 60 to 120. The calculator is a timing tool, not a medical one, so it gives no advice on how much sleep any age group needs.
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