Sleep Calculator
Wake up refreshed by timing your sleep in complete 90-minute cycles. Enter your wake-up time to see ideal bedtimes, or your bedtime to see ideal alarm times.
Go to bed at one of these times:
9:45 PM
6 cycles · 9 hrs
Recommended
11:15 PM
5 cycles · 7.5 hrs
12:45 AM
4 cycles · 6 hrs
2:15 AM
3 cycles · 4.5 hrs
Based on 90-minute sleep cycles plus ~15 minutes to fall asleep. Waking between cycles helps you feel more rested.
🔒 This tool runs entirely in your browser. Your data is never uploaded.
Frequently asked questions
How does it pick bedtimes?＋
It works around 90-minute sleep cycles, so you wake at the end of a cycle rather than mid-cycle when you feel groggy.
Why 90 minutes?＋
A full sleep cycle averages about 90 minutes, and waking between cycles tends to feel more refreshing.
Is this a guarantee?＋
No — cycle length varies by person and night, so treat the times as helpful targets.