Sleep Calculator
Find the bedtime or alarm time that wakes you between sleep cycles.
Wake Up Between Cycles, Not In The Middle Of One
Sleep runs in cycles of about ninety minutes, moving from light sleep into deep sleep and back up to dreaming. Waking at the end of a cycle feels natural; an alarm that goes off in deep sleep leaves you groggy for half the morning, even after the same total hours.
Tell the calculator when you need to get up and it suggests bedtimes that fit whole cycles, allowing for the time it takes you to fall asleep. Or tell it when you are going to bed and it suggests alarm times. Cycle length varies between people, so you can adjust it until the times suit you.
Key features
- Two directions — bedtimes for a wake-up time, or wake-up times for a bedtime.
- Adjustable cycle length — from 70 to 120 minutes.
- Time to fall asleep — added automatically, 15 minutes by default.
- Right now — one tap for going to bed immediately.
- Age-aware recommendation — highlights the number of cycles most people your age need.
This tool runs entirely inside your browser using native Web APIs. Your files and text are never uploaded to a server, never logged and never shared with third parties.
How to use: Sleep Calculator
- Choose the direction
I need to wake up at…, or I am going to bed at…. - Enter the time
Or press Right now if you are heading to bed. - Adjust if you know your sleep
How long you take to drop off, and your cycle length. - Pick a time
Five or six cycles is right for most adults.
Technical specifications
| Processing location | Entirely in your browser — no server round trip |
|---|---|
| Data uploaded | None. Files and text never leave your device |
| Price | Free — no account, no trial, no usage cap |
| Category | Calculators |
| Works offline | Yes, once the page has loaded |
| Browser support | Chrome 90+, Edge 90+, Firefox 90+, Safari 15+ |
| Interface languages | English, 中文, हिन्दी, Español, العربية |
Frequently asked questions
How long is a sleep cycle?
About 90 minutes on average, but anywhere from 70 to 120 minutes is normal, and cycles tend to be shorter early in the night and longer toward morning. If the suggested times leave you groggy, try adjusting the cycle length a little.
How many hours of sleep do I need?
Most adults need seven to nine hours — five or six cycles. Teenagers need eight to ten, and school-age children nine to eleven. Older adults need about the same as other adults, although sleep often becomes lighter.
What if I wake up during the night?
Brief awakenings between cycles are normal and usually not remembered. If you are awake for a long time, the cycle timing restarts from when you fall asleep again.
How long should a nap be?
Either about 20 minutes, which stays in light sleep, or a full cycle of about 90 minutes. Anything in between risks waking from deep sleep and feeling worse than before.
Is this a substitute for treating a sleep problem?
No. Cycle timing helps you wake more easily; it does not fix insomnia, snoring or daytime sleepiness, which are worth discussing with a doctor.