Sleep Cycle Calculator
Find the best bedtime or wake-up time based on 90-minute sleep cycles.
How to Use the Sleep Cycle Calculator
- Choose whether you want to plan around a wake-up time or a bedtime.
- Enter that time.
- You'll see several options, each a whole number of 90-minute sleep cycles apart, so you wake up between cycles instead of mid-cycle.
Frequently Asked Questions
Why 90 minutes for a sleep cycle?
A full sleep cycle — moving through light sleep, deep sleep, and REM sleep — takes about 90 minutes on average, though it genuinely varies from about 70 to 120 minutes between individuals and even between cycles in the same night. 90 minutes is the commonly used average that sleep calculators are built around.
Why does waking up between cycles matter?
Waking up in the middle of a deep sleep stage tends to cause grogginess ("sleep inertia"), while waking up at the boundary between cycles, during lighter sleep, tends to feel more natural and alert. Timing your sleep in full 90-minute cycles aims to land your wake-up at one of those lighter boundaries.
What's the 14-minute buffer for?
It accounts for the average time it takes a person to actually fall asleep after getting into bed, so the cycle math starts from when you're likely asleep rather than from when you lie down.
Is this a substitute for medical sleep advice?
No — this is a general guideline based on average cycle length, not a personalized or medical sleep assessment. If you have ongoing sleep problems, consult a doctor or sleep specialist.