Sleep Calculator
Find the optimal time to go to bed based on when you need to wake up. We calculate backwards in 90-minute sleep cycles and add 14 minutes for you to fall asleep.
Enter your wake-up time and click calculate to see your optimal bedtimes.
How this calculator works
Human sleep isn't uniform. We sleep in cycles that last roughly 90 minutes. During these cycles, we move through light sleep, deep sleep, and REM (Rapid Eye Movement) sleep.
If you wake up in the middle of a deep sleep stage, you're more likely to feel groggy and disoriented for a while — a phenomenon known as "sleep inertia." Sleep timing, sleep quality, accumulated sleep debt, and other factors can all affect how rested you feel.
Our sleep calculator works backwards from your desired wake-up time in 90-minute blocks, aiming to place your alarm near the end of a cycle rather than in the middle of one. Because cycle length varies between people and across the night, treat these times as a starting point to test, not a precise prediction.
Frequently Asked Questions
Why is 14 minutes added to the calculation?
Studies show the average adult takes between 10 to 20 minutes to fall asleep (called sleep latency). We use 14 minutes as a conservative average so you can simply get into bed at the recommended time.
What if my sleep cycles aren't exactly 90 minutes?
90 minutes is a planning convention, not a fixed biological length — the NHLBI notes that a new cycle starts roughly every 80 to 100 minutes, and cycles often get longer as the night progresses. This calculator provides a solid baseline to experiment with. Adjust by 15-minute increments if you find it's consistently off for your body.
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Sources
General information about sleep stages and cycles is based on published guidance from the National Heart, Lung, and Blood Institute (NIH). Sleep duration recommendations are based on guidance from the CDC.