You slept for 8 hours, yet you feel like you were hit by a truck. Meanwhile, your friend slept for 6 hours and is bouncing off the walls. The difference isn't just the hours—it's the cycles.
Time Your Wake Up Call
Stop guessing. Find out exactly when to set your alarm to wake up in between cycles, not during them.
Open Sleep Calculator →1. The 90-Minute Rule
Sleep isn't a single long block. It's a series of 90-minute waves. Each wave takes you through light sleep, deep sleep, and REM (Rapid Eye Movement) sleep. Waking up at the end of a cycle (e.g., after 7.5 hours) feels great. Waking up in the middle of deep sleep (e.g., after 8 hours) leaves you with "sleep inertia"—that heavy, groggy feeling.
2. Quality > Quantity
While 8 hours is the standard advice, 7.5 hours (5 complete cycles) is often better than 8. If you sleep 8 hours, you are likely waking up right in the middle of your 6th cycle's deep sleep phase. This is why sometimes "sleeping in" makes you feel worse.
3. The Power Naps
If you can't get a full night's sleep, hack the system with naps:
- 10-20 Minutes: Power nap. Good for alertness and energy. You stay in light sleep.
- 60 Minutes: Avoid this. You enter deep sleep and will wake up groggy.
- 90 Minutes: Full cycle. Good for creativity and emotional memory.
4. Sleep Hygiene Math
It takes the average person 14 minutes to fall asleep. When you calculate your wake-up time, you need to add this "buffer" time. If you need to be up at 7:00 AM, and you want 5 cycles (7.5 hours), you shouldn't go to bed at 11:30 PM. You should be in bed by 11:16 PM.
5. The "Social Jetlag"
Staying up late on weekends shifts your internal clock. If you sleep 11 PM - 7 AM on weekdays, but 2 AM - 10 AM on weekends, you are essentially flying across 3 time zones every Friday night and flying back every Sunday. No wonder Mondays hurt.
Calculate Your Bedtime
Don't do the mental math while you're tired. Use our Sleep Calculator to count backwards from your wake-up time and find the perfect moment to hit the pillow.