🛌 Sleep Calculator
Our free Sleep Calculator helps you find the best bedtime and wake-up times based on natural 90-minute sleep cycles. By aligning your schedule with your body’s circadian rhythm, you can wake up refreshed instead of groggy.
Find Your Best Bedtime
Select your desired wake-up time, and we’ll calculate bedtimes that let you complete full sleep cycles.
💡 Most adults need 4–6 full sleep cycles (about 6–9 hours). Pick the option that best fits your routine.
Find Your Best Wake-Up Time
If you know when you’re going to bed, this calculator shows the best wake-up times that avoid cutting off a sleep cycle.
💡 Waking up at the end of a cycle leaves you refreshed. Aim for 5–6 cycles (7.5–9 hours).
How the Sleep Calculator Works
Sleep happens in repeating 90-minute cycles, moving through Stage 1, Stage 2, Deep Sleep, and REM Sleep. Waking up in the middle of a cycle can leave you feeling tired. Our calculator adds a 15-minute buffer for falling asleep and then works backward or forward in 90-minute intervals.
Recommended Sleep Cycles
Most adults need 7–9 hours of sleep, or about 5–6 full cycles. Shorter nights may mean only 3–4 cycles, but aligning wake-up times with the end of a cycle is more important than the total hours.
- 3 cycles → ~4.5 hours (not ideal, but better than interrupted sleep)
- 4 cycles → ~6 hours
- 5 cycles → ~7.5 hours (healthy range)
- 6 cycles → ~9 hours (ideal for many adults)
FAQs About Sleep Cycles
❓ Is 6 hours of sleep enough?
6 hours covers about 4 sleep cycles, which may be enough for some people, but most adults function better with 7–9 hours.
❓ Why do I feel groggy after 8 hours?
You may have woken up in the middle of a cycle. Using a sleep calculator helps you wake up at the right time.
❓ Should I always aim for 90-minute multiples?
Yes — waking at the end of a cycle is better than interrupting one, even if total sleep time is shorter.
❓ How many sleep cycles do adults need per night?
Most adults need 4–6 full cycles (about 6–9 hours). Children and teens often need more.