Calculating the right bedtime is more important than simply “going to bed early.” If you wake up in the middle of a sleep cycle, you’ll feel groggy even after 10 hours in bed. However, if you time your wake-up call for the end of a cycle, 7.5 hours is plenty to feel fully refreshed.
How does the 90-minute sleep rhythm work? Below, I’ve put together a reference table to help you wake up energized every morning.
Our sleep consists of repeating cycles, each lasting approximately 90 minutes. Within each cycle, there is a deep sleep phase, where it is very difficult to wake up, and a REM (Rapid Eye Movement) phase, which is when we dream. If your alarm goes off during deep sleep, you’ll feel “heavy” and exhausted, regardless of how many hours you slept. But if you wake up at the end of a cycle, your body is already primed to rise, and getting out of bed feels effortless.
The first cycle doesn’t start the second you close your eyes. On average, it takes about 15 minutes to actually fall asleep. Therefore, when calculating your bedtime, you need to add those 15 minutes to your lights-out time and count from that point.
Table: When to Hit the Hay to Wake Up Refreshed
The table below shows the optimal bedtimes for your desired wake-up time. It is calculated for 5 full cycles (7.5 hours of sleep) and 6 full cycles (9 hours of sleep), plus a 15-minute window to fall asleep. Choose the option that works best for your lifestyle.
| Wake-Up Time | Bedtime (7.5 hrs sleep) | Bedtime (9 hrs sleep) |
| 5:00 AM | 9:15 PM | 7:45 PM |
| 6:00 AM | 10:15 PM | 8:45 PM |
| 6:30 AM | 10:45 PM | 9:15 PM |
| 7:00 AM | 11:15 PM | 9:45 PM |
| 7:30 AM | 11:45 PM | 10:15 PM |
| 8:00 AM | 12:15 AM | 10:45 PM |
| 8:30 AM | 12:45 AM | 11:15 PM |
| 9:00 AM | 1:15 AM | 11:45 PM |
These numbers are a guide. If you need more time to fall asleep (e.g., 30 minutes), move your bedtime up by those 30 minutes. If you pass out instantly, you can head to bed a bit later. The key is to maintain the number of full cycles.
Why You Shouldn’t Just “Sleep for 8 Hours”
Eight hours is roughly 5.3 cycles. If you go to bed at 11:00 PM and set your alarm for 7:00 AM, you’ll likely wake up in the middle of your sixth cycle. The result is brain fog, a headache, and the urge to sleep for another hour. It is much better to aim for 7.5 hours (5 cycles) or 9 hours (6 cycles). This way, the alarm goes off at the transition between cycles, allowing you to wake up easily.
What if You Can’t Stick to the Table?
Sometimes work or other life circumstances make it impossible to hit the ideal time. In these cases, try at least to avoid waking up mid-cycle. Count back 7.5 or 9 hours from your wake-up time and add 15 minutes. If you have to go to bed at a different time, don’t sweat it. Just be prepared for a potentially rough morning. However, your body will adapt quickly if you stick to the same cycle for several days in a row.
Extra Tips for Healthy Sleep
Put away your gadgets an hour before bed. The blue light from screens suppresses melatonin—the sleep hormone. Crack a window; sleeping in a cool room is much more effective. Try to avoid caffeine in the afternoon. And remember: even the most perfectly calculated schedule won’t help if your room is noisy or too bright.
Experiment. One person might feel great after 5 cycles (7.5 hours), while another needs 6 (9 hours). Monitor how you feel for a week. If you’re following the table but still feel tired, try increasing or decreasing the number of cycles by one. Everyone has their own unique “normal.”
Most importantly, don’t blow your routine on the weekends. If you go to bed at 11:15 PM during the week but stay up until 2:00 AM on Saturday, your internal clock will get thrown off, and the table will stop working. Try to keep any shifts in your schedule to no more than an hour.
Now you know how to calculate the perfect moment to call it a night. Use the table, listen to your body, and start waking up with a smile.
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