Slumber

Find the best time to fall asleep — or wake up.

Slumber is an offline sleep-cycle calculator: pick when you want to wake up and it works backward through 90-minute cycles to the times you should fall asleep, so you wake between cycles instead of mid-dream — or flip it to plan your wake-up from a bedtime. Each option shows the exact time, how many cycles and hours of sleep it buys, and which choices are best rested. Built end-to-end with AI, it runs entirely in your browser with no login, and the whole single-file source is downloadable to self-host or remix.