Free Sleep Calculator

Find the best bedtime or wake time based on 90-minute sleep cycles.

Sleep occurs in roughly 90-minute cycles through different sleep stages — waking up mid-cycle (during deep sleep) tends to feel groggier than waking at a cycle boundary. This is a general guideline based on typical cycle length; individual cycle length varies somewhat.

Worked Example

Example: Waking at 6:30 AM, going to bed at 10:15 PM allows for 5 full 90-minute cycles (7.5 hours) plus time to fall asleep.

Formula / Method

Works backward/forward from your target time in 90-minute increments (a typical sleep cycle length), showing several cycle-aligned options plus ~15 minutes to account for falling asleep.

Worked Example

Example: Waking at 6:30 AM, going to bed at 10:15 PM allows for 5 full 90-minute cycles (7.5 hours) plus time to fall asleep.

Formula / Method

Works backward/forward from your target time in 90-minute increments (a typical sleep cycle length), showing several cycle-aligned options plus ~15 minutes to account for falling asleep.