Sleep Calculator
Find a better bedtime or wake-up time based on 90-minute sleep cycles. Choose when you want to wake up or when you plan to go to bed.
Calculate sleep cycles
Choose a wake-up time or bedtime and compare 4, 5 and 6 cycle options.
Choose a mode and enter a time to see 4, 5 and 6 cycle options.
Quick sleep calculator examples
How the sleep calculator works
The calculator uses 90-minute sleep cycle estimates. If you choose a wake-up time, it counts backward to suggested bedtimes. If you choose a bedtime, it counts forward to suggested wake-up times.
What is a sleep cycle?
A sleep cycle is often estimated at about 90 minutes. That is a useful planning shortcut, but real cycles can be shorter or longer and may change during the night.
Bedtime based on wake-up time
When you know when you need to wake up, use the wake-up mode. The calculator suggests bedtimes for 4, 5 and 6 cycles, with an optional 15-minute buffer for falling asleep.
Wake-up time based on bedtime
When you already know when you plan to go to bed, use the bedtime mode. The calculator suggests wake-up times after 4, 5 and 6 estimated cycles.
Common sleep calculator mistakes
Assuming every sleep cycle is exactly 90 minutes
The 90-minute cycle is an estimate. Your actual sleep cycles can vary by night, age, schedule, stress, caffeine, light and other everyday factors.
Forgetting time needed to fall asleep
If it usually takes you a while to fall asleep, include the 15-minute buffer so the suggested bedtime is earlier than the start of the first cycle.
Choosing too few cycles regularly
Four cycles may be useful for comparison, but many adults commonly aim for around 7 to 9 hours of sleep. Individual sleep needs vary.
Treating the calculator as medical advice
This is a practical planning tool, not medical advice. If sleep problems affect your day-to-day life, consider speaking with a qualified professional.
Free online sleep calculator
This sleep calculator helps you plan a bedtime or wake-up time using simple 90-minute sleep cycle estimates. It is useful when you know when your alarm needs to ring, when you know when you plan to go to bed, or when you want to compare several practical options before choosing one.
Results are estimates, not guarantees. Sleep cycles are commonly described in roughly 90-minute blocks, but actual sleep changes from person to person and from night to night. The optional 15-minute buffer helps account for time spent settling down before sleep begins.
Why results are estimates
A calculator can do the time math, but it cannot know exactly how long your sleep cycles will be, how quickly you fall asleep or how rested you will feel. Adults often need around 7 to 9 hours of sleep, but needs vary. Use the results as planning suggestions and adjust them based on your own schedule and experience.
Sleep Calculator FAQ
How does a sleep calculator work?
A sleep calculator counts forward or backward in 90-minute sleep cycle blocks from your chosen bedtime or wake-up time.
What is a 90-minute sleep cycle?
A 90-minute sleep cycle is a common estimate for a full sleep cycle. Real sleep cycles vary from person to person and across the night.
Should I include time to fall asleep?
Include the 15-minute buffer if you want bedtime suggestions to account for a little time before sleep begins.
How many sleep cycles should I get?
The calculator shows 4, 5 and 6 cycles. Many adults aim for roughly 7 to 9 hours of sleep, but individual needs vary.
Is this sleep calculator medical advice?
No. This calculator is a planning tool based on approximate sleep cycles and is not medical advice.
Is my sleep data stored?
No. The calculation runs locally in your browser and your times are not uploaded or stored.
Is this calculator free?
Yes. The sleep calculator is free to use and works directly in your browser.