Tell us when you plan to go to bed, or when you have to be up, and we will work out the times that land on the end of a sleep cycle rather than the middle of one.
Go to sleep at
five full cycles from an 11:30 pm bedtime — 7 h 30 m of sleep
4 cycles · 6 h 00 m5:44 am
5 cycles · 7 h 30 m7:14 am
6 cycles · 9 h 00 m8:44 am
Lights out
11:30 pm
Asleep by
11:44 pm
Cycle length
90 minutes
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.
Most adults take somewhere around 14 minutes to fall asleep, so if you get into bed at 11:30 pm the cycle clock starts at about 11:44 pm. From there:
Cycles
Time asleep
Wake at
4
6 h 00 m
5:44 am
5
7 h 30 m
7:14 am
6
9 h 00 m
8:44 am
For most people going to bed at 11:30, the five-cycle option is the realistic one: 7 h 30 m of sleep, up at 7:14. Four cycles gets you up at 5:44 am, which is early enough that you would be short on sleep rather than well-timed — cycle timing does not compensate for not enough of it.
What a sleep cycle actually is
Through the night you move repeatedly from light sleep into deep slow-wave sleep and then into REM, and back out again. One full pass is a cycle. Waking at the end of one means waking out of light sleep, which generally feels less awful than an alarm going off in the middle of deep sleep. That is the whole idea this page is built on, and it is worth being clear that it is a rule of thumb rather than a precision instrument.
Methodology
A cycle is modelled at 90 minutes, the conventional average, and 14 minutes is added for sleep onset. Bedtime plus onset gives the start of cycle one; each option is that time plus a whole number of 90-minute cycles. No other assumptions are involved — this is arithmetic on a clock, not a model of your physiology.
Limitations, stated plainly
Ninety minutes is a population average, not your number. Real cycles run roughly 70 to 120 minutes, and they change through the night: early cycles carry more deep sleep and later ones more REM, so they are not interchangeable blocks. That means the fifth boundary is a much wider target than the first, and the arithmetic gets less precise as the night goes on. Fourteen minutes to fall asleep is likewise an average and can be wildly wrong on any given night.
Total sleep matters more than boundary timing. If the choice is between six cycles at an awkward hour and five cycles at a sensible one, take whichever gets you enough sleep on a schedule you can actually keep. Waking mid-cycle occasionally is not a problem worth engineering around.
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 a sleep cycle?
About 90 minutes on average, which is the figure this calculator uses. Individually they range from roughly 70 to 120 minutes, and yours are not the same length all night — the first cycles of the night are weighted towards deep slow-wave sleep and the later ones towards REM. So 90 minutes is a reasonable planning number and a poor prediction of any specific cycle.
Why does the calculator add 14 minutes?
Because you do not fall asleep the moment you get into bed. Fourteen minutes is a commonly used average for sleep onset in adults. If you reliably drop off in two minutes, or reliably lie awake for forty, adjust the field — it shifts every result by the same amount.
Is it really better to wake at the end of a cycle?
Waking from light sleep generally feels better than being pulled out of deep sleep, and that difference is real. But it is a smaller effect than simply getting enough sleep, and the 90-minute figure is too approximate to hit a boundary reliably five cycles out. Treat this as a way to choose between a 7:15 and an 8:45 alarm, not as a reason to accept less sleep in exchange for better timing.
How many hours of sleep do I need?
Five to six cycles — roughly 7.5 to 9 hours — is the range most adults settle into, and it is the range this calculator highlights. Four cycles (6 hours) is on the short side for most people. We are not going to tell you what is right for you; how you feel after a fortnight of a consistent schedule is far better evidence than any calculator.
Does this work for naps?
Not directly — a nap is usually either much shorter than a cycle (20 minutes, staying in light sleep) or one full cycle (90 minutes). The awkward zone is 40 to 70 minutes, which tends to land you in deep sleep when the alarm goes. Use the nap calculator for that.
Why do different sleep calculators give different times?
Mostly because of the sleep-onset allowance. Some sites use 14 minutes, some 15, some 20, and some add nothing at all. A site adding nothing will give you times exactly 14 minutes earlier than this one. The cycle length is near-universally 90 minutes, so that part rarely differs.