Sleep Calculator
Free sleep calculator: find the best time to go to bed or wake up based on 90-minute sleep cycles and your age, so you wake up refreshed.
Quick times
Enter a time above to see your sleep schedule.
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Free Sleep Calculator
Tell the calculator when you need to wake up — or when you are heading to bed — and it works out the times that fall at the end of a 90-minute sleep cycle, so you wake during light sleep instead of being jolted out of deep sleep. It shows several cycle options at once, factors in the time it takes you to fall asleep, and flags which options meet the recommended hours for your age.
What Is a Sleep Cycle?
During the night your body moves through repeating sleep cycles of light sleep, deep sleep, and REM, each lasting about 90 minutes on average. A good night is typically 4 to 6 complete cycles. Waking at the end of a cycle — when sleep is lightest — leaves you feeling refreshed, while waking mid-cycle (especially out of deep sleep) is what makes you groggy even after 8 hours. The formula below works backward from your wake time.
Bedtime formula
Bedtime = Wake time − (cycles × 90 min) − time to fall asleepHow to Use the Sleep Calculator
Choose whether you are setting a wake-up time or a bedtime.
Enter the time (or tap a quick preset, or Use current time for sleeping now).
Pick your age group and how long you usually take to fall asleep.
Review the suggested times — each shows the number of cycles and total sleep.
Pick a time inside the recommended range and set your alarm or bedtime.
When a Sleep Calculator Helps
Setting an alarm
Find the bedtime that lets you wake at your alarm at the end of a cycle, not in the middle of deep sleep.
Going to bed now
Tap Use current time to see the best moments to set your alarm if you fall asleep right now.
Fixing groggy mornings
If you wake tired even after enough hours, aligning wake-up to a cycle boundary often helps.
Early starts
Planning a 5 a.m. flight or shift? Work back to the bedtime that still gives you full cycles.
Kids and teens
Check the recommended hours by age and find a bedtime that meets them for school nights.
Shift work
Plan sleep around irregular hours by counting cycles instead of guessing.
Why Use Our Sleep Calculator?
Both directions in one tool
Work out your bedtime from a wake-up alarm, or your wake time from when you go to bed — plus a one-tap option for going to sleep right now.
All cycle options side-by-side
See 4, 5, and 6-cycle times together (6, 7.5, and 9 hours) and pick the one that fits your schedule, instead of a single fixed answer.
Age-aware guidance
We highlight which options meet the National Sleep Foundation recommended hours for your age, from newborns to older adults.
Accounts for falling asleep
Nobody falls asleep instantly. Adjust the time it takes you to drift off (default 15 minutes) so the suggested times are realistic.
See the cycles
A simple timeline shows your night split into cycles, so it is clear why waking at a cycle boundary matters.
Free, private, no sign-up
Everything runs in your browser. No account, no ads in your face, no data leaving your device.
Sleep Calculator FAQ
Count back from your wake time in 90-minute blocks and add the time it takes you to fall asleep. For a 6:30 a.m. alarm with 15 minutes to drift off, good bedtimes are about 9:15 p.m. (6 cycles, 9 hours) or 10:45 p.m. (5 cycles, 7.5 hours). The calculator does this for you.
Most adults do best with 5 to 6 complete cycles, which is 7.5 to 9 hours of sleep. Four cycles (6 hours) can work occasionally but is below the recommended range for adults.
You were likely woken in the middle of a cycle — often during deep sleep — rather than at the lighter end of one. Timing your wake-up to a cycle boundary usually reduces that grogginess (called sleep inertia).
Most people take around 10 to 20 minutes. The calculator uses 15 minutes by default, and you can change it so the suggested times match how quickly you actually drift off.
Per the National Sleep Foundation: newborns 14–17 hours, infants 12–15, toddlers 11–14, preschoolers 10–13, school-age 9–11, teens 8–10, adults 7–9, and older adults 7–8 hours.
Six hours (4 cycles) is below the 7–9 hours recommended for adults. It may get you through a day, but regularly sleeping that little builds sleep debt and hurts focus, mood, and health.
No — 90 minutes is an average. Real cycles range from roughly 80 to 110 minutes and vary between people and across the night. The calculator uses 90 minutes as a reliable starting point.
Many people feel noticeably less groggy when they wake at the end of a cycle during light sleep. It is a helpful rule of thumb, though total sleep duration and consistency still matter most.