Bedtime Calculator — Sleep Cycle Timer

Calculate the best bedtime based on 90-minute sleep cycles. Get browser reminders that work even when the tab is closed.

Stop waking up groggy. Time your sleep to the cycle — not the clock. Most people think 8 hours of sleep is enough. It's not that simple. Waking up in the middle of a deep sleep cycle leaves you feeling worse than if you'd slept 7.5 hours and finished the cycle cleanly. The difference isn't how long you sleep — it's when your alarm goes off. How the sleep calculator works: Your brain moves through 90-minute sleep cycles all night. Each cycle includes light sleep, deep slow-wave sleep, and REM sleep. This extension counts backwards from your target wake-up time in 90-minute increments, adds 14 minutes for average sleep onset, and gives you the four best times to go to bed tonight. Enter your wake-up time and get your ideal bedtime in one click.