About SleepCalculator

SleepCalculator is a free tool that helps you plan your sleep around 90-minute sleep cycles. Instead of counting raw hours, it works out bedtimes and wake-up times that land at the end of a cycle — the moments when waking up feels easiest.

How it works

Enter the time you need to wake up, and the calculator counts backwards in 90-minute cycles, adding ~14 minutes for the average time it takes to fall asleep. Prefer to sleep right now? The reverse mode lists the wake-up times that give you complete cycles from the moment you go to bed.

Our mission

Millions of people wake up groggy every morning simply because their alarm lands in the middle of a deep-sleep phase. We built this simple tool to fix that one calculation — free, with no sign-up, no apps to install, and no data collected about you.

Disclaimer

Individual sleep cycles vary between roughly 70 and 120 minutes, so treat our results as smart starting points, not medical guidance. For persistent sleep problems, please see a healthcare professional.