How to use the Sleep Calculator
- Choose whether you know your wake-up time or your bedtime.
- Enter the time and how long you usually take to fall asleep.
- Pick one of the suggested times — 5 or 6 cycles is ideal for most adults.
Why 90 minutes?
Sleep runs in cycles of roughly 90 minutes, moving from light sleep to deep sleep and REM. Waking at the end of a cycle usually feels easier than being woken from deep sleep. Five cycles is 7.5 hours and six is 9 hours; most adults need 7–9 hours.
Cycle length varies between people and through the night, so treat the times as a starting point.
Also searched as: bedtime calculator, what time should i go to bed, when should i wake up, sleep cycle calculator, wake up time calculator.
Tools that pair well with the Sleep Calculator
- Pomodoro Timer — Work in focused 25-minute sessions with short breaks, and a long break every four.
- Countdown Timer — Set a countdown in seconds — type hours, minutes and seconds or tap a preset — and get an alarm sound and an optional notification when it reaches zero.
- World Clock — See the current time in cities around the world side by side, with the time difference from you and whether it’s day or night.
- Time Duration Calculator — Find the time between two clock times (even past midnight), or add up durations like 1:45 + 2:30 — in hours and minutes and decimal hours.
Frequently asked questions
How many sleep cycles do I need?
Most adults feel best after five or six cycles (7.5–9 hours).
Why add time to fall asleep?
It usually takes 10–20 minutes to fall asleep, so cycles start after you get into bed.
Is anything I enter saved or sent?
No. The calculation runs in your browser. Your last inputs are remembered on this device only, so the page opens where you left off.
Can I install Sleep Calculator as a web app and use it offline?
Yes. Sleep Calculator is an installable web app (PWA) — installed from your browser, not downloaded from an app store. Click Install app at the top of this page in Chrome or Edge (Windows, macOS, Linux, ChromeOS) or on Android, use Share → Add to Home Screen on iPhone and iPad, or File → Add to Dock in Safari 17+ on a Mac. It then opens in its own window with its own icon, and because it runs entirely in your browser it keeps working offline. Firefox on desktop can’t install web apps. How installing works.