Sleep Calculator
Find the perfect bedtime or wake-up time based on sleep cycles.
How does the sleep calculator work?
The sleep calculator uses the science of sleep cycles. A full sleep cycle lasts approximately 90 minutes, and waking up at the end of a cycle leaves you feeling refreshed. The calculator adds or subtracts full 90-minute cycles (plus an average 15 minutes to fall asleep) to your chosen time. For example, if you need to wake up at 7:00 AM, it suggests bedtimes at 9:45 PM (5 cycles), 11:15 PM (4 cycles), or 12:45 AM (3 cycles). Choose the option that best fits your schedule.
How to use the Sleep Calculator
Select either "I want to wake up at…" to get suggested bedtimes, or "I plan to go to bed at…" to see optimal wake-up times. Enter your target time and click "Calculate". The tool displays 3–4 options based on 90-minute sleep cycles, each labeled with the number of complete cycles. Pick the time that works best for your routine.
Example calculation
If you want to wake up at 7:00 AM, recommended bedtimes: 9:45 PM (5 cycles, 7.5 h), 11:15 PM (4 cycles, 6 h), 12:45 AM (3 cycles, 4.5 h), 2:15 AM (2 cycles, 3 h). The calculator includes 15 minutes to fall asleep, so the actual sleep duration is always a multiple of 90 minutes.
Frequently Asked Questions
Are 90‑minute sleep cycles the same for everyone?
Sleep cycles typically range from 80 to 120 minutes, with 90 minutes being the average for most adults. The calculator uses 90 minutes as a reliable guideline. For more personalized tracking, consider using a sleep tracker or smartwatch that monitors your actual cycles.
Why is 15 minutes added for falling asleep?
The average person takes about 10–20 minutes to fall asleep after getting into bed. The calculator includes this typical latency so that your actual sleep cycles align with the suggested times. If you usually take longer or fall asleep immediately, adjust the results slightly.