Sleep Calculator
Sleep works in 90-minute cycles. Wake up between cycles — not in the middle — and you will feel fresh instead of groggy.
Go to sleep at one of these times:
Set your alarm for one of these times:
Times include about 15 minutes to fall asleep. 6 cycles (9 hours) is ideal for most adults; 5 cycles (7.5 hours) is a good minimum. This is an estimate for information only — not medical advice.
How to use
- Pick a mode: plan bedtime from a wake-up time, or plan wake-up from a bedtime.
- Choose one of the big time cards — the green one is recommended.
- Keep a regular schedule for the best results.
Frequently Asked Questions (FAQ)
How does the sleep calculator work?
Sleep runs in 90-minute cycles. The calculator finds times when you would wake up between cycles, so you wake up fresh instead of groggy.
What are the two modes of the calculator?
In wake-up mode you set the time you must get up and get the best bedtimes. In sleep mode you set when you are going to sleep and get the best alarm times.
What does the green recommended card mean?
The green card marks the option closest to 6 sleep cycles, about 9 hours in bed, which is the ideal amount for most adults. All cards include about 15 minutes to fall asleep.
Why does waking up at the wrong time feel so bad?
Waking up in the middle of a 90-minute cycle, especially during deep sleep, interrupts the cycle and causes grogginess. Timing your alarm to a cycle boundary avoids this.