Never wake up mid-cycle again.
Tell this calculator your wake up time or your bedtime and it counts backward or forward in full 90 minute cycles. You get four options with the two closest to a full night's rest marked, plus a night arc that shows exactly where each one falls.
Set one time, land on the end of a cycle.
Tell the calculator what you already know: when you need to wake up, or when you are heading to bed. It counts backward or forward in full 90 minute cycles from there, live as you change any value.
Most adults need 10 to 20 minutes to drift off once they lie down.
To wake at 06:30, go to bed by 21:15 or 22:45.
Go to bed by
How it works.
- Choose whether you know your wake up time or your bedtime, and set it.
- Move the slider to how many minutes it usually takes you to fall asleep.
- Read the four cards and the arc: the two closest to a full night are marked.
What a 90 minute cycle is
Sleep runs in loops of light sleep, deep sleep and REM, and one full loop lasts about 90 minutes, though the true figure for any person on any night sits between 70 and 120 minutes. Most adults complete four to six of these loops in a night, which is why 6 cycles works out at 9 hours and 3 cycles at 4 hours 30 minutes. Waking inside deep sleep, the heaviest stage of the loop, produces the foggy feeling some call sleep inertia. Waking near the boundary between one cycle and the next, once the body has already drifted back towards lighter sleep, tends to feel far less abrupt. That difference in how a morning feels is one reason rest shows on the face before anything else does, a link covered in our guide to what comes before cosmetics.
Where the numbers come from
The 90 minute figure traces back to sleep laboratory work that first mapped the ultradian rhythm of a night's sleep, and it has held up as a useful average since, even though individual cycles vary by 20 to 30 minutes either way. This calculator adds one more number before the first cycle starts: sleep latency, the 5 to 30 minutes it typically takes to drift off once you lie down, with most adults landing between 10 and 20 minutes. Move the slider to match your own habit and every bedtime or wake time shifts to account for it. The same logic, working backward from a fixed point in the evening, is worth applying to the whole wind down, and not just the final minutes, which is the idea behind our spa day guide.
What this tool is not
These four options are an average built from population data, not a reading of your own sleep. Some people cycle closer to 70 minutes, others closer to 110, and the gap between the two grows across a night, so a plan built for 6 cycles can be 30 to 60 minutes off by the last one. Shift workers, frequent flyers and anyone with a diagnosed sleep disorder such as insomnia or sleep apnoea need a different approach entirely, ideally with a clinician rather than a calculator. If mornings regularly leave you with puffy eyes or persistent fatigue no matter which bedtime you choose, that is worth raising with a doctor rather than solving with an earlier alarm.
Frequently asked.
Why 90 minutes and not a round number?
90 minutes is the average length of one full loop through light sleep, deep sleep and REM. Your own cycles might run between 70 and 120 minutes, but 90 plans a useful night for most adults.
Should I trust the 6 cycle option over the 3 cycle one?
6 cycles, 9 hours, and 5 cycles, 7 hours 30 minutes, sit inside the 7 to 9 hours most adults need, so those two are marked as recommended. 4 and 3 cycles are shorter nights for when the clock will not allow more, not a nightly target.
Why does the time to fall asleep matter?
Every bedtime already has those extra minutes built in. If you actually take 20 minutes to drift off but the slider is set to 15, each cycle after that lands later than planned, so matching it to your own habit keeps the wake time accurate.
What is the arc showing?
Your night drawn as one curve from bedtime to wake time, split into segments. The wide segment nearest sunrise is the base 3 cycles every plan shares, and each extra segment toward the moon adds one more full cycle.
I do not sleep in neat 90 minute blocks. Is this still useful?
It is a starting point, not a measurement of your own sleep. If you consistently feel worse at the times it suggests, your own cycles likely run shorter or longer than average, and a week of notes will tell you more than any calculator.
Does this tool save or send my times anywhere?
No. Every calculation happens in your browser as you type, nothing is sent anywhere, and closing the tab clears it.
Guides behind this tool
Skin and Cosmetics
Radiance: what comes before cosmetics
Skin and Cosmetics
Puffy eyes: cold works, caffeine helps
Wellness
Spa day: the order makes the differenceMore tools
The Sleep Cycle Calculator estimates bedtimes and wake times from an average 90 minute cycle. It does not diagnose insomnia, sleep apnoea or any other sleep disorder, and it is not a substitute for a clinician. This page is for general information and does not replace medical or professional cosmetic advice.