Sleep Calculator
Find the ideal bedtime or wake time based on 90-minute sleep cycles.
How to use this tool
- Choose a desired wake time or a target bedtime.
- See the recommended cycle-based times.
- Pick the one that fits your schedule.
How it works
Working back from wake time, multiples of 90 minutes (plus a ~15 min fall-asleep allowance) generate bedtimes; reversing gives wake times.
Tips
- Consistency beats finding the 'perfect' number — keep the same sleep window.
- Use the 6-cycle wake time to feel freshest for big days.
Limitations
Individual cycle length varies; it's a heuristic for waking less groggily, not a sleep science guarantee.
Frequently asked questions
What is the 90-minute cycle theory?
Sleep moves through cycles averaging about 90 minutes; waking mid-cycle leaves you groggy. Aiming to wake at a cycle boundary helps.
How many hours should adults sleep?
Most adults need 7-9 hours — typically 5-6 full cycles.
What's the 15-minute rule?
Add 15 minutes after a cycle to fall asleep, which the calculator factors into the 'ideal times' math.