Sleep Calculator
Find the best times to wake up or go to bed based on 90-minute sleep cycles — waking between cycles means you feel more refreshed.
What Does This Tool Do?
Find the optimal bedtime or wake-up time based on 90-minute sleep cycles. Waking at the end of a complete cycle means you feel more rested — this calculator shows all options with the recommended 6-cycle timing highlighted.
Key Features
Sleep Cycles
Based on 90-minute REM/NREM cycle science.
Both Directions
Find bedtime from wake-up, or vice versa.
Recommended
Highlights the ideal 6-cycle (7.5 hr) option.
Full Table
All cycle options shown simultaneously.
How to Use
- Select Find Bedtime or Find Wake-Up Time.
- Enter your wake-up time or intended sleep time.
- Click the button to see all optimal sleep times.
Frequently Asked Questions
Why 90 minutes?▾
The average human sleep cycle is approximately 90 minutes, cycling through light sleep, deep sleep and REM. Waking mid-cycle causes grogginess (sleep inertia).
How many hours of sleep do I need?▾
Most adults need 7–9 hours (5–6 cycles). The calculator highlights 6 cycles (7.5 hrs) as the recommended target for most people.
Why add 14 minutes?▾
The average person takes about 14 minutes to fall asleep after lying down. This is subtracted from the target to get the recommended bedtime.