Ninety minutes is an average, not your number. This version lets you set the cycle length and see how much the answer moves.
Wake at
five cycles of 90 minutes from an 11:30 pm bedtime
4 cycles · 6 h 00 m—
5 cycles · 7 h 30 m7:14 am
6 cycles · 9 h 00 m—
Lights out
11:30 pm
Asleep by
11:44 pm
Cycle length
90 minutes
If your cycles are not 90 minutes, five of them from this time end at:
Five cycles at different cycle lengths
Cycle length
Five cycles ends
80 min
6:24 am
90 min
7:14 am
100 min
8:04 am
This calculator needs JavaScript to recalculate. The answer shown above was worked out when the page was built and is correct for the date in the address bar.
Last checked
Why make the cycle length adjustable
Every sleep calculator on the internet hard-codes 90 minutes and prints times to the minute. Both of those things cannot be right at once. Cycle length varies between people, roughly 70 to 120 minutes, and varies within one night for the same person. Making the number editable is the honest version of this tool, and it lets you see something the fixed-90 calculators hide: how much the answer moves when the assumption moves.
Worked example: the sensitivity, from an 11:30 pm bedtime
Cycle length
Five cycles ends at
80 minutes
6:24 am
90 minutes
7:14 am
100 minutes
8:04 am
A 10-minute error in the cycle length moves the five-cycle wake time by 50 minutes. That is the single most useful fact on this page, and it is the reason to treat any cycle-boundary alarm time as a 45-minute window rather than a minute. It is also why the sixth cycle is a much rougher target than the second: errors compound with every cycle.
How to estimate your own cycle length
You cannot measure it properly without a lab, and consumer wearables infer sleep stages from movement and heart rate rather than measuring brain activity, so their stage data is an estimate of an estimate. The practical approach: keep a fixed wake time for a fortnight and notice which alarm times leave you groggy. If 7:15 consistently feels worse than 6:30 from the same bedtime, your cycles are probably shorter than 90 minutes. That is weak evidence, and we are not going to dress it up as anything stronger.
Methodology
Wake time = bedtime + sleep onset + (cycle length × number of cycles). Defaults are 90 minutes per cycle and 14 minutes to fall asleep. Both are editable, which is the entire point of this page as distinct from the main sleep calculator.
Limitations
Cycles are not a fixed length within one night. The early cycles of the night carry more deep slow-wave sleep and the later ones more REM, and the later ones tend to run slightly longer. A single cycle-length setting therefore cannot be right for the whole night, which puts a floor under how accurate any calculator of this kind can be. Nothing here can tell you your actual cycle length.
This page does arithmetic on sleep cycles. It is not medical advice and nothing here is a claim about health.
Common questions
How long is my sleep cycle?
Probably somewhere between 70 and 120 minutes, and not the same all night. There is no way to find out precisely without polysomnography. Consumer trackers estimate sleep stages from movement and heart rate rather than measuring brain activity, so their cycle data is indicative at best. Ninety minutes is the sensible default for planning.
How much does the cycle length change the answer?
A lot, and this is worth internalising. From an 11:30 pm bedtime, five cycles ends at 6:24 am if your cycles are 80 minutes and 8:04 am if they are 100 — a 100-minute spread from a 20-minute assumption. Errors compound with each cycle, so treat any cycle-boundary time as a window of about three quarters of an hour.
Is a sleep cycle the same as a REM cycle?
People use the terms interchangeably but they are not the same thing. A full cycle passes through light sleep, deep slow-wave sleep and REM. REM is one phase within the cycle, and it takes up a larger share of each cycle as the night goes on. When a calculator says “cycle” it means the whole pass, not the REM portion.
Why do the early cycles and late cycles differ?
Deep slow-wave sleep is front-loaded — most of it happens in the first two or three cycles of the night. REM is back-loaded, so later cycles contain proportionally more of it and tend to run a little longer. This is why waking after four cycles is not simply “two-thirds as good” as waking after six; the parts you miss are not the same as the parts you got.
Should I set the cycle length based on my fitness tracker?
You can, but weight it accordingly. Wrist trackers infer stages from movement and heart-rate variability. They are reasonable at telling you when you were asleep and much weaker at telling you which stage you were in. If your tracker consistently reports a cycle length far from 90 minutes, that is worth a try in this field; it is not worth treating as a measurement.