It's Not Just About 8 Hours

We've all been told that 8 hours is the "gold standard" for sleep. However, have you ever slept for 9 hours and woken up feeling groggy, but felt surprisingly refreshed after only 6 hours? The answer lies in Sleep Cycles.

The Science of 90 Minutes

Human sleep isn't a single, flat state. Instead, we transition through several stages throughout the night, usually in cycles of approximately 90 minutes. These stages include light sleep, deep sleep, and REM (Rapid Eye Movement) sleep.

Waking up during deep sleep—the most physically restorative stage—is what causes "sleep inertia," that heavy, disoriented feeling that can last for hours after you get out of bed.

Waking Up Refreshed

The secret to waking up with high energy is to time your alarm so it goes off at the end of a 90-minute cycle.

Common target durations include:

• 7.5 hours (5 cycles)
• 9 hours (6 cycles)
• 6 hours (4 cycles)

How to Plan Your Sleep

1. Pick a Wake-Up Time: Determine when you absolutely need to be out of bed.
2. Count Backward: Subtract 90-minute blocks from that time.
3. Factor in Fall-Asleep Time: The average person takes about 14-15 minutes to actually fall asleep. Don't forget to add this to your math!

Our Sleep Calculator does this math for you automatically, giving you the perfect bedtimes to ensure you wake up at the peak of your cycle.