WatchTimeAbout WatchTime Online
WatchTime Online is an independent collection of free time and date utilities, built and maintained by a solo web developer in Massachusetts, USA.
Why the site exists
Time questions are among the most common things people look up — what time is it in Tokyo, how many days until an event, what does this timestamp mean — and the answers are simple. Yet the sites that answer them are often heavy, cluttered, and vague about how they arrive at their results. WatchTime Online was built on the opposite premise: one page per question, an answer above the fold, and an explanation of the method underneath so you can verify it yourself.
Principles
Client-side by default
Every calculator runs in your browser. Birthdays, deadlines, and timestamps you type are never transmitted to a server or stored by the site.
Documented methods
Each tool states the conventions it uses — ISO 8601 week rules, calendar-clamping for month arithmetic, IANA time zone data — because a result you can't reproduce is a result you can't trust.
Fast and quiet
Pages are plain HTML with a small amount of JavaScript. No accounts, no pop-ups, no newsletter prompts. Advertising keeps the site free; it's limited to standard display units and never interstitials.
Accuracy and data sources
Clocks on this site read your device's system time, which modern operating systems synchronize to internet time servers (NTP). Time zone and daylight saving rules come from your browser's implementation of the IANA time zone database, which browser vendors update as governments change their rules. Calendar arithmetic follows the proleptic Gregorian calendar as implemented by ECMAScript's date facilities. If you spot a result that looks wrong, please report it — reproducible bug reports get fixed.
The name
"WatchTime" is meant literally: a place to watch the time — your own, and everyone else's around the world. The orange mark in the logo is the seconds hand.