Sleep Calculator — When Should You Go to Sleep?
Calculate your ideal bedtime based on when you need to wake up. Align with natural 90-minute sleep cycles for better rest and easier waking.
Sleep occurs in 90-minute cycles alternating between light sleep deep sleep and REM sleep. Waking during deep sleep causes grogginess while waking at the end of a cycle feels refreshing. The ideal sleep duration is 5-6 complete cycles (7.5-9 hours) including the 15 minutes it typically takes to fall asleep. Planning your bedtime around these cycles can dramatically improve how you feel in the morning.
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Sleep Calculator
Key Information
| Parameter | Details |
|---|---|
| Sleep Cycle Length | 90 minutes (average) |
| Recommended Cycles | 5-6 per night |
| Recommended Duration | 7.5 - 9 hours |
| Time to Fall Asleep | 15 minutes (average) |
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Use Calculator NowFrequently Asked Questions
What time should I go to bed to wake at 7am?
To wake at 7:00 AM feeling refreshed count backwards in 90-minute cycles plus 15 minutes to fall asleep. 6 cycles (9 hours) = go to bed at 9:45 PM. 5 cycles (7.5 hours) = go to bed at 11:15 PM. 4 cycles (6 hours — minimum) = go to bed at 12:45 AM. The 11:15 PM and 9:45 PM options are best for most adults.
How many hours of sleep do I need?
Adults 18-64 need 7-9 hours. Older adults 65+ need 7-8 hours. Teenagers need 8-10 hours. While some people claim to function on 6 hours research shows that less than 7 hours consistently leads to cognitive decline immune suppression and increased disease risk even if you feel fine. Only about 1% of people have a genetic mutation allowing genuine short sleep.
Why do I feel tired after 8 hours of sleep?
You likely woke during a deep sleep phase rather than at the end of a cycle. Eight hours is 5.33 cycles which means waking mid-cycle. Try 7.5 hours (5 complete cycles) or 9 hours (6 complete cycles) instead. Other causes include sleep apnea poor sleep quality inconsistent schedule blue light exposure before bed and caffeine consumption after 2 PM.
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Last updated: March 2026