Every holiday date on this site is computed from a rule, not copied from a list. This page says which rule, how confident we are in each answer, and what we deliberately leave out.
The eleven US federal holidays
Set by 5 U.S.C. section 6103: New Year's Day, Martin Luther King Jr. Day, Washington's Birthday (commonly Presidents' Day), Memorial Day, Juneteenth National Independence Day, Independence Day, Labor Day, Columbus Day, Veterans Day, Thanksgiving and Christmas Day. Six are fixed dates and five are floating — the third Monday in January, the third Monday in February, the last Monday in May, the first Monday in September, the second Monday in October and the fourth Thursday in November. These are the only holidays that make a day non-working in our business-day calculations.
The observed-date rule
When a fixed-date federal holiday falls on a Saturday it is observed on the preceding Friday; when it falls on a Sunday, on the following Monday. Our business-day counts skip the observed date, because that is the day offices are actually shut. One consequence catches people out: when 1 January falls on a Saturday, the federal closure is 31 December of the previous year.
What we do not include
State holidays, bank holidays, court holidays, school holidays and company holidays. They vary by jurisdiction and by employer, and a calculator that silently folded one set in would be wrong for most of the people using it. If your deadline runs on a state or court calendar, that calendar is the authority, not this site.
Movable Christian dates
Easter Sunday is the first Sunday after the first ecclesiastical full moon falling on or after 21 March, computed with the Gregorian anniversary computus. That puts it between 22 March and 25 April. Good Friday is two days before, Palm Sunday seven days before, Ash Wednesday forty-six days before and Mardi Gras forty-seven. Eastern Orthodox Easter applies the same rule on the Julian calendar and usually lands on a different date; we do not currently publish it.
Jewish observances
The Hebrew calendar has been a fixed arithmetic calendar for roughly a thousand years, so Rosh Hashanah, Yom Kippur, Passover and Hanukkah are computed exactly, not estimated. What the pages do say is that each observance begins at sunset on the evening before the date shown, which is the part a Gregorian date cannot express.
Islamic observances are estimates, and are labelled as such
The start of Ramadan and Eid al-Fitr depend on the local sighting of the crescent moon. Any date published in advance is a prediction, and it can differ by a day between countries in the same year. We compute the tabular Islamic calendar — the standard arithmetic approximation — and every page carrying one of these dates says plainly that it is an estimate. We would rather be visibly uncertain than confidently wrong.
Astronomical dates
Equinoxes and solstices are computed from Meeus's solar-longitude algorithm, accurate to well under a minute for any year we cover, and reported in UTC. The time zone matters more than it looks: the September 2026 equinox falls at 00:05 UTC on the 23rd, which is the evening of the 22nd across the United States. An equinox is an instant, not a day.
The one date with no algorithm behind it
Diwali. It falls on the new moon of the Hindu month of Kartika, which needs an ephemeris we do not carry, and regional traditions mark different days of the five-day festival as the main one. Our Diwali dates come from a short hand-entered table rather than a computation, they are marked as approximate on the page, and they are the one part of this data set we would not want anyone to rely on for a booking. Everything else here is derived.
Coverage and review
Countdown dates are computed for 2026 to 2032. The rules themselves are reviewed annually, and any change in federal holiday law would be applied at the next rebuild. The date arithmetic is verified on every build against an independent reference implementation, including hand-checked anchor dates for the computus, the Hebrew calendar and the solstices.