Sleep Cycle built a following on one specific piece of math: sleep runs in roughly 90-minute cycles, and waking up between cycles instead of in the middle of one is the difference between feeling rested and feeling wrecked. You do not need motion-tracking or a microphone on your nightstand to use that math. So we built Wake Cycle, a free sleep calculator that runs the same 90-minute logic right here in your browser. Enter a time and the recommended options appear instantly.
Work out your sleep cycles
It opens with your current time already filled in, so there is a real answer on screen before you touch anything.
How to use it
Pick a mode at the top: “Going to bed” if you are turning in now and want to know when to wake up, or “Wake up at” if you have a fixed alarm and want to know when to fall asleep. Set the time with the field below, or tap Now to jump straight to the current time. Every change updates the list and the clock immediately. There is no calculate button.
The list below shows four options, from 3 to 6 sleep cycles, each with the resulting clock time and how many hours of sleep it represents. The 24-hour ring above it plots the same options around a clock face, with your anchor time marked at the center and the two more rested options picked out in indigo. Your last time and mode are saved on your device, so they are already there next time you open the page. Nothing leaves your browser.
How it compares to Sleep Cycle
Wake Cycle does one job: turn a bedtime or a wake-up time into a short list of cycle-aligned options, instantly, on anything with a browser. The full Sleep Cycle app does much more. It listens through your phone’s microphone and accelerometer to detect which cycle you are actually in overnight, wakes you inside a smart window near your alarm instead of at a fixed minute, and logs your real sleep history with snore detection and trend charts over weeks and months.
We kept the core loop: the 90-minute cycle math and the instant, editable output. We left out the overnight tracking entirely, because that requires a phone on your mattress all night and a persistent background process, not a calculator you check for ten seconds while you’re already planning your evening.
Our honest take: use Wake Cycle when you are deciding what time to set an alarm for, or explaining cycle-based sleep timing to someone else without asking them to install anything. Get the full Sleep Cycle app when you want it to detect your actual sleep stages overnight and wake you at the right moment automatically, not just calculate a suggested one in advance.
Get the full app
Sleep Cycle by Northcube AB is free to download on Android, with a Premium tier that adds snore analysis, sleep aid sounds, and extended sleep history. If subscription pricing has you looking elsewhere, we’ve also rounded up our tested picks for the best Sleep Cycle alternatives.
Frequently asked questions
How does a sleep cycle calculator work?
It counts backward or forward from a time you enter in blocks of 90 minutes, which is roughly how long one full sleep cycle lasts, plus about 15 minutes to account for the time it takes most people to actually fall asleep. Waking up at the end of a cycle rather than in the middle of one is generally what makes a shorter night feel more rested than a longer one that cuts a cycle short.
Can I use this instead of Sleep Cycle’s alarm?
For working out a bedtime or a wake-up time in advance, yes. Sleep Cycle’s alarm goes further: it tracks your movement overnight to detect which cycle you are actually in and wakes you inside a window near your set time, rather than at a fixed minute you picked ahead of time. This calculator gives you the target times; the app adapts to what actually happens that night.
Is this the official Sleep Cycle app?
No. Wake Cycle is an original tool we built, inspired by the 90-minute cycle math that Sleep Cycle popularized. It is not affiliated with, endorsed by, or connected to Northcube AB. If you want overnight tracking, snore detection, and sleep history, get the official app from the store links above.
Does it work offline and is it free?
Yes to both. It is completely free with no signup, and once the page has loaded it keeps working without a connection. Your last time and mode are saved in your browser’s local storage on your device only.
How many sleep cycles should I aim for?
Most adults do well with 5 to 6 full cycles a night, which works out to roughly 7.5 to 9 hours of sleep. Four cycles, about 6 hours, is a workable minimum on a short night, and 3 cycles is closer to a long nap than a full night’s rest. The calculator marks 5 and 6 cycles as recommended so you can see them at a glance.
