Sleep Calculator
Wake up refreshed by timing your sleep to complete 90-minute cycles. Tell it when you want to wake up and it shows the best bedtimes — or set a bedtime to get good wake-up times. It allows ~15 minutes to fall asleep. Runs in your browser.
FAQ
How does the sleep calculator work?
Sleep runs in ~90-minute cycles; waking at the end of one feels more refreshing than mid-cycle. Enter your wake time for bedtimes that complete full cycles (plus ~15 min to fall asleep), or enter a bedtime for good wake times.
How many cycles do I need?
Most adults do best on 5-6 cycles (~7.5-9 hours). The tool highlights those and also lists 4 cycles.
Why am I tired after 8 hours?
Often the alarm interrupts deep sleep mid-cycle. Timing wake-up to a cycle's end can help you feel more rested.
Is the 90-minute cycle exact?
It's an average (~80-110 min, varying through the night) — a helpful guide, not a guarantee.
More tools: online timer, Pomodoro timer, and the full tools list.