About timeinusa.net

How the clocks are computed

Every clock on this site is calculated in your browser, using three standard sources — no time is fetched from our server.

Time zone rules come from the IANA time zone database (tzdb), the same reference used by operating systems worldwide. Your browser ships it built in and exposes it through the standard Intl.DateTimeFormat API; each page simply names its zone (for example America/Chicago), and the browser applies the correct UTC offset and daylight saving rule for this exact moment.

Sunrise, sunset, and day length are computed from each city's coordinates with the NOAA solar position equations, accurate to about a minute. They are calculated fresh for today's date every time a page loads.

The current moment comes from your device clock, which your operating system keeps synchronized to atomic time via NTP. The clocks here are therefore exactly as accurate as your device — typically within a fraction of a second.

What this site does not do

There are no cookies, no analytics, no ads, no fingerprinting, and no third-party requests of any kind. The only things your browser downloads are this site's own HTML, one stylesheet, and one small script. Nothing you do here is recorded — see the privacy policy for the full statement.

The site also does not try to guess where you are. Each page shows the time for the place named on the page, not for your location.

Spotted an error?

Time zone boundaries and DST rules occasionally change. If a page here disagrees with reality — a wrong zone, a stale DST date, a sunrise off by more than a couple of minutes — please get in touch. Background reading: how the US zones work and the DST calendar.