Sleep Calculator
Wake up refreshed by timing your sleep to complete 90-minute cycles. Find the best bedtime or wake-up time, plan naps, track sleep debt, and set reminders.
What is a Sleep Calculator?
A Sleep Calculator helps you time your sleep around natural 90-minute cycles. Tell it when you want to wake up, or when you plan to sleep, and it suggests times that let you finish complete cycles so you wake during light sleep feeling rested.
How to Use the Sleep Calculator
Choose a mode: find a bedtime from your wake-up time, find a wake-up time from your bedtime, sleep now, or plan a nap. Adjust how long you take to fall asleep and your cycle length if needed, then calculate. The best option is highlighted for you.
Why 90-Minute Cycles Matter
Sleep runs in repeating stages, and the full loop takes about 90 minutes.
5 cycles = 7.5 hours (recommended)
6 cycles = 9 hours
Bedtime = Wake-up − cycles − time to fall asleep
Example Calculation
What This Calculator Shows
Simple Habits for Better Sleep
Keep a consistent schedule, even on weekends. Avoid screens and bright light in the hour before bed, keep your room cool and dark, and cut caffeine after early afternoon. Reserve the bed for sleep so your body links it with rest, and get morning sunlight to set a steady body clock.
Frequently Asked Questions
A Sleep Calculator works out the best times to fall asleep or wake up so you complete full 90-minute sleep cycles. Waking at the end of a cycle instead of the middle helps you feel more refreshed and less groggy.
During the night you move through repeating cycles of light sleep, deep sleep, and REM sleep. Each cycle lasts about 90 minutes, and most adults need four to six complete cycles per night.
If your alarm goes off in the middle of deep sleep you wake up disoriented and tired. Timing your wake-up to the end of a 90-minute cycle means you rise during lighter sleep, which feels far more natural.
Most adults do best with five to six cycles, roughly 7.5 to 9 hours. Five cycles (7.5 hours) is the widely recommended sweet spot, which is why the calculator highlights it as the best option.
A 20-minute power nap boosts alertness without grogginess. A 90-minute nap completes a full cycle and can leave you feeling refreshed. Avoid the 45-to-60-minute range, which often ends in deep sleep.
Sleep debt is the running total of sleep you missed compared with what your body needs. The calculator estimates your debt over the last seven nights and suggests how much earlier to go to bed to recover.