Use the Sleep Calculator
Work out when to go to bed or wake up based on 90-minute sleep cycles so you wake refreshed. Enter a wake time or bedtime and get the best times.
- Free to use
- No signup
- Nothing to install
- Runs in your browser
Illustration. Open the tool for the real thing.
What is the Sleep Calculator?
Sleep runs in cycles of about 90 minutes. Waking in the middle of a cycle leaves you groggy, while waking at the end feels natural. Tell the calculator when you need to wake up and it suggests the bedtimes that complete whole cycles.
You can also enter a bedtime, or use 'sleep now', to see the best wake-up times. The calculation allows about 15 minutes to fall asleep.
3 steps to your result
Open the tool and follow along. Nothing to install.
What you get
Times aligned to 90-minute cycles.
Find bedtime or find wake-up time.
Best wake times if you go to bed now.
Change the time to fall asleep.
AZRS tools are free to open and use.
It opens in your browser, so there is nothing to download.
Used for
Pick one to see how it fits.
How it compares
A plain look at this tool next to the usual alternative.
| This calculator | Desktop software | |
|---|---|---|
| Install | Nothing to install | Usually an app or program to install |
| Account | No signup | Depends on the product |
| Cost | Free to use | Free or paid, depends on the product |
| Where it runs | In your browser tab | On your computer |
Questions people ask
How many hours of sleep do I need?
Most adults need 7 to 9 hours, which is 5 to 6 full sleep cycles.
What is a sleep cycle?
A repeating pattern of light, deep and REM sleep that lasts roughly 90 minutes.
Why allow 15 minutes to fall asleep?
That is the average time most people need to drift off.
Is this medical advice?
No. It is a planning aid. Talk to a doctor about sleep problems.
How long is a sleep cycle?
About 90 minutes, moving through light, deep and REM sleep.
More free tools
Related to the Sleep Calculator.