Sleep Cycle Calculator
Find the best times to go to bed or wake up, timed to complete 90-minute sleep cycles so you rise between cycles instead of mid-cycle.
I want to
The time your alarm goes off.
How long you usually take to drift off after getting into bed. Starts at 15.
Clock format
Everything is calculated in your browser. Nothing is uploaded.
Times end a full 90-minute cycle, which feels more refreshing than waking mid-cycle. Includes about 15 minutes to fall asleep.
How to calculate the best time to sleep or wake up
Choose a mode
Pick whether you want to wake up at a set time or are heading to bed right now.
Set the time
Enter your wake-up time, or let the tool read the current time when you are going to bed now.
Adjust fall-asleep time
Set how long you usually take to drift off, which starts at 15 minutes.
Read the recommended times
The ranked list shows bed or wake times for 4, 5, and 6 full sleep cycles with the total sleep in each.
Why use this tool
Timed to full sleep cycles
Every suggestion lands at the end of a 90-minute cycle, so you wake between cycles rather than in the middle of deep sleep.
Two ways to plan
Work backward from a fixed wake-up time, or forward from the moment you go to bed to see when you will naturally wake.
Counts your fall-asleep time
A separate field adds the minutes it takes you to drift off, starting at 15, so the schedule reflects real time in bed.
Ranked with total sleep
Each option is labelled with its cycle count and total sleep length, and the healthier 7.5 to 9 hour nights are highlighted.
Handles times past midnight
Bedtimes and wake times that cross midnight are wrapped to the correct clock time, so a 6am alarm still points at the right evening.
Runs entirely in your browser
Everything happens on your device; nothing is uploaded.
About this tool
A night of sleep is made of repeating cycles of light sleep, deep sleep, and REM, each lasting roughly 90 minutes. Waking in the middle of a cycle, especially during deep sleep, is what leaves you groggy, while waking at the end of one feels far more natural. This calculator lines your alarm up with the end of a cycle. Tell it when you need to wake up and it counts backward to show the bedtimes that give you 4, 5, or 6 complete cycles; tell it you are going to bed now and it counts forward to the matching wake-up times.
Because most people do not fall asleep the instant their head hits the pillow, a fall-asleep field of 15 minutes by default is added on top of the cycle maths, so the times reflect real time in bed. Six cycles is about 9 hours and five is about 7.5 hours, the range most adults do best on, so those options are highlighted; four cycles, roughly 6 hours, works as a shorter night. Times that run past midnight are wrapped to the correct clock time.
Everything is worked out on your device as you type, so nothing you enter is uploaded or stored. If you would rather count down to a fixed moment, the countdown timer does that, and the pomodoro timer handles focus blocks during the day.
Frequently asked questions
- How does the sleep cycle calculator work?
- It builds a schedule from 90-minute sleep cycles. From a wake-up time it counts backward, and from your bedtime it counts forward, adding the minutes you take to fall asleep, then lists the times that complete 4, 5, or 6 whole cycles.
- Why 90-minute cycles?
- A full sleep cycle averages about 90 minutes for most adults, though it can range from roughly 70 to 120 minutes and shift through the night. Ninety minutes is the standard estimate, so the results are a close guide rather than a medical measurement.
- Should I aim for 4, 5, or 6 cycles?
- Most adults feel best on 5 to 6 cycles, which is about 7.5 to 9 hours, so those are highlighted as recommended. Four cycles, roughly 6 hours, works as a shorter night when a full sleep is not possible.
- What is the fall-asleep time for?
- It is the time you usually spend drifting off after getting into bed, set to 15 minutes by default. The tool adds it to the cycle maths so the suggested times reflect when you are actually asleep, not just lying down.
- Does it handle times after midnight?
- Yes. Bedtimes and wake times that cross midnight are wrapped to the correct clock time, so working backward from an early morning alarm still lands on the right evening.
- Is my data uploaded anywhere?
- No. Everything runs in your browser; nothing is sent to a server.
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