DaysUntilNowHoliday dates and the rules behind them
Some dates you look up. These have to be worked out — from a lunar table, a statute, an astronomical instant or a weekday pattern — which is exactly why calendars disagree about them.
Clock change date calculator
Five rulebooks, and two windows a year when the Atlantic gap is an hour out.
Friday the 13th finder
Twelve thirteenths, seven weekdays, and a limit no year has ever broken.
Holiday observed date calculator
The legal date and the day off are two different dates, and only one of them moves.
Same calendar year finder
An old wall calendar is only useless until the pattern comes round again.
Season start date calculator
Two definitions, two dates, and neither of them is the 21st every year.
When is Easter calculator
The one holiday that has to be calculated before anyone can look it up.
Which one you need
You want a date and it moves. When is Easter runs the computus for any year from 1583 onwards, in both the Western and the Orthodox tradition, and hands you Ash Wednesday, Good Friday, Ascension and Pentecost with it. Season start dates gives the exact instant of each equinox and solstice, in either hemisphere, next to the meteorological date that weather services use instead.
You want to know which day you actually get off. Holiday observed dates applies the federal weekend rule in both directions — a Saturday holiday moves back to the Friday, a Sunday holiday forward to the Monday — and lists all eleven federal holidays for the year so you can see at a glance whether anything shifts.
You want to know when the clocks change. Clock change dates derives the dates from each jurisdiction’s law rather than from a list, which is also how it can tell you exactly how long the transatlantic time difference is an hour out.
You are chasing a pattern rather than a date. Friday the 13th counts every one in any year and finds the next from today; same calendar years tells you which other years share a year’s entire weekday grid, and which parts of it will not come with them.
Four kinds of rule, four kinds of surprise
A lunar table. Easter is fixed to an ecclesiastical moon rather than the real one, which is why it can be calculated centuries ahead and why it can still disagree with the sky.
A statute. Observed days off and clock changes are decided by legislation, so they change when a parliament says so and not before. Two governments writing sensible rules independently produced the three-week gap between the American and European clock changes.
An astronomical instant. Equinoxes and solstices happen at a moment, not on a day. The date depends on where you are standing, and it drifts because a tropical year is not a whole number of days.
A weekday pattern. Friday the 13th and repeating calendars are pure arithmetic on the seven-day week and the leap rule — no astronomy, no law, and no exceptions until a century year that is not a leap year arrives.
Where these sit on the rest of the site
Every date in this group also turns up in the holiday date table, which lays out everything this site tracks in one place with the weekday each date falls on. If you would rather watch a date approach than look it up, the countdowns recount to the second in your own time zone.
For the arithmetic underneath — how far apart two dates are, how many working days a stretch contains, what week number today is — see date calculators and calendar tools.
Frequently asked questions
Which of these dates change every year, and which only look as though they do?
Two of them genuinely move: Easter, because it follows an ecclesiastical lunar table, and the equinoxes and solstices, because they are astronomical instants that drift against a calendar of whole days. The rest only appear to move. Clock changes, observed days off and Friday the 13th all come from rules that never change at all — the second Sunday in March, the Friday before a Saturday holiday, the 13th of the month — and it is the weekday grid underneath them that shifts from year to year.
Why do two calendars disagree about the same holiday?
Usually because they are answering different questions with the same words. A printed calendar shows the legal date of a holiday and a payroll system shows the day the office is closed; a forecaster’s first day of spring is the first of the month and an almanac’s is the equinox; a Western and an Orthodox Easter come from the same rule applied to two different calendars. None of them is wrong, and each tool in this group tells you which convention it is using rather than picking one silently.
Do these calculators cover holidays outside the United States?
Partly, and each page says where the line falls. Easter, the seasons, Friday the 13th and repeating calendars are not national at all. Clock changes cover the United States and Canada, the European Union, the United Kingdom and Ireland, Australia and New Zealand as separate rule sets. Observed days off use the eleven US federal holidays and 5 U.S.C. 6103, with the British substitute-day rule shown alongside for comparison — state, local and private-employer calendars differ from all of them.
How we calculate this
Every date in this group is derived from its rule at the moment you ask, rather than read out of a stored list. Easter uses the computus, the seasons use the periodic-terms method for the equinox and solstice instants, clock changes and observed days off use the nth-weekday rules named in the relevant legislation, and the calendar-pattern tools use the Gregorian leap rule.
That choice has one practical consequence worth stating: nothing here can run out or go stale. A published table of Easters or clock changes ends at whatever year its author stopped typing, and the years past the end look identical to the years before it.
Where a rule is set by law rather than by arithmetic — the American clock change, the federal observed day — future years assume the current law stays in force. That is the only assumption in this group, and it is a political one rather than a mathematical one.
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