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Time To Celebrate

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How we calculate

Every date on this site comes from one date engine. It handles fixed dates, "nth weekday of the month" holidays, dates counted from Easter, and the equinoxes and solstices that start the seasons.

Holidays

US holiday rules follow federal law (5 U.S.C. 6103). When a federal holiday falls on a Saturday it is observed on Friday, and on Monday when it falls on a Sunday.

Easter

Western Easter is computed with the standard Gregorian algorithm (the computus). Mardi Gras, Ash Wednesday and Good Friday are counted back from it.

Seasons

Equinox and solstice times are calculated with the method from Jean Meeus's Astronomical Algorithms and agree with published times to within a few minutes. Season countdowns run to that exact moment; the calendar date can differ by a day depending on your time zone.

Counting days

"Days until" counts whole calendar days in your own time zone: tomorrow is 1 day away, whatever the time is now. The hours, minutes and seconds run to local midnight at the start of the day.

Pre-rendered numbers

Each page is built with the day count as of its build date so the answer is in the page itself. As soon as the page loads, the timer switches to your device's clock.

Where the calculation happens

In your browser. The page downloads the tool once and does the work on your device, so results appear as you type and your inputs are not sent to us.

What a tool page shows

  • The date the page was last updated.
  • How the result is produced.
  • On the tools rebuilt on our current template: the formula or rule, a worked example you can check by hand, and the sources the numbers come from, linked. Older tools are being brought up to that standard.

Sources we rely on

Limits

Dates are calculated for the Gregorian calendar and, for holidays, for the United States unless a page says otherwise. Employers, schools and states decide their own days off; check with them before you plan around a holiday.