Going to bed now, or at a set time? These are the alarm times that land at the end of a sleep cycle instead of the middle of one.
Set your alarm for
five full cycles from an 11:00 pm bedtime — 7 h 30 m of sleep
4 cycles · 6 h 00 m5:14 am
5 cycles · 7 h 30 m6:44 am
6 cycles · 9 h 00 m8:14 am
Lights out
11:00 pm
Asleep by
11:14 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.
Allowing 14 minutes to fall asleep, cycle one starts at 11:14 pm.
Cycles
Time asleep
Alarm at
4
6 h 00 m
5:14 am
5
7 h 30 m
6:44 am
6
9 h 00 m
8:14 am
Five cycles is the option that fits a normal working morning. Six gets you a fuller night if you can start late enough; four is the one to pick only when the alternative is a shorter night still.
If you are going to bed right now
The most common version of this question is asked at 11:47 pm by someone who has already decided to stop scrolling. Set the bedtime field to the current time and the four-cycle row is usually the one that matters — it is the answer to “how bad is this going to be”, and knowing the alarm lands at a cycle boundary is a small consolation that costs nothing.
Methodology
Cycles are modelled at 90 minutes and sleep onset at 14 minutes. Wake time = bedtime + 14 minutes + (90 minutes × number of cycles). That is the entire calculation.
Limitations
Ninety minutes is an average; real cycles run about 70 to 120 minutes and lengthen as the night goes on, so the sixth boundary is a far looser target than the second. Fourteen minutes to fall asleep is also an average and is the single biggest source of error on a bad night. Total sleep matters more than boundary timing, so do not trade an hour of sleep for a better-timed alarm.
This page does arithmetic on sleep cycles. It is not medical advice and nothing here is a claim about health.
Common questions
What time should I wake up if I go to bed now?
Enter the current time as your bedtime and take the highest cycle count that still gets you up in time. Because sleep onset takes around 14 minutes, an alarm at exactly six or seven and a half hours from now will land slightly early — the calculator accounts for that.
Is 6 hours of sleep enough?
Six hours is four cycles, so it at least ends on a boundary, which is why it appears in the table. Whether it is enough for you is a question this page cannot answer and will not pretend to. Most adults settle between five and six cycles. If you are consistently choosing four, the timing is not the part worth optimising.
Why is the wake time not exactly 7.5 hours after my bedtime?
Because 14 minutes is added for falling asleep. Bedtime is when you get into bed; the cycle clock starts when you are actually asleep. If you drop off faster than that, reduce the sleep-onset field and every result shifts earlier by the same amount.
Should I set my alarm for the end of a cycle or just get more sleep?
More sleep, nearly every time. The boundary effect is real but small, and 90 minutes is too rough an average to hit a boundary reliably several cycles out. Use this to choose between two alarms that are both acceptable, not to justify a shorter night.
Does hitting snooze ruin the timing?
Ten minutes of dozing after an alarm does not start a new cycle, so the arithmetic on this page is unaffected. It also will not give you meaningful extra rest — the interrupted light sleep you get from a snooze cycle is not the same thing as a continuous cycle.