Sleep Cycle Calculator
Free sleep cycle calculator. 100% client-side.
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What is Sleep Cycle Calculator?
The Sleep Cycle Calculator plans the best bedtime or wake-up time using 90-minute sleep cycles. It works in two modes - backwards from a target wake-up time, or forwards from "sleep now" - and adds a 15-minute fall-asleep buffer. The cycle length is adjustable between 60 and 120 minutes for people whose personal cycle is shorter or longer than average.
Key Benefits
- Two clear modes for bedtime and wake-up planning
- Adjustable cycle length to match your personal rhythm
- Recommended 5-6 cycle options highlighted for best rest
- No signup, no tracking, no network calls
- Works fully offline in any modern browser
Common Use Cases
- •Plan the night before for a 7:00 alarm
- •Decide when to set the alarm if you go to bed right now
- •Adjust a personal sleep cycle length tracked by a wearable
- •Plan for a shift, travel, or jet-lag recovery schedule
- •Test how a 60- vs 90-minute cycle changes your sleep window
How to use the Sleep Cycle Calculator
- Pick a mode: Choose "wake at" to plan backwards from a target wake-up time, or "sleep now" to see when to set your alarm from the current moment.
- Enter your time: Type the desired wake-up time in wake-at mode, or the time you are going to sleep in sleep-now mode. Use the "Now" button to reset to the current time.
- Adjust the cycle length if needed: The default is 90 minutes. Drag the slider if you know your personal cycle length is shorter or longer (60–120 min).
- Read the four suggested times: Pick one of the four suggested bedtimes or wake times. The two highlighted options (5–6 full cycles) let you wake up at the end of a sleep cycle and feel most rested.
Key Features
- Dual mode: target wake-up time or "sleep now"
- Calculates 3–6 full sleep cycles (4.5–9 hours)
- Adjustable sleep cycle length slider (60–120 min)
- Recommended cycle highlighting for best rest
- 15-minute fall-asleep buffer applied automatically
- 100% client-side, works fully offline, no tracking
Frequently Asked Questions
What is a 90-minute sleep cycle?
A sleep cycle is one full pass through the stages of sleep (light, deep, and REM). On average it lasts about 90 minutes, and most adults go through 4–6 cycles per night. Waking at the end of a cycle usually feels easier than waking in the middle of deep sleep.
Why does the calculator add 15 minutes?
Most people need about 10–20 minutes to fall asleep. We subtract those 15 minutes from your available sleep window in "wake at" mode, so the suggested bedtime is when you should actually be heading to bed, not when your head hits the pillow.
Can I change the cycle length?
Yes. The default is 90 minutes, but you can adjust it between 60 and 120 minutes in 5-minute steps. If you track your sleep with a wearable and know your personal cycle length, use that value for more accurate results.
Is my sleep data sent anywhere?
No. The calculator runs entirely in your browser. The times you enter and the results shown never leave your device, so your sleep schedule stays private.