Defining the Holidays (calendar calcs)

I called our HR department, expecting that they use a formula to decide which days are our official holidays from year to year, i.e., let’s say we get New Years Day, MLK, Prez Day, Good Friday, Mem Day, 4th of July, Labor Day, Columbus, Thanksgiving + the Friday following, and a string starting Dec 24 for Christmas. (goyish conventional?)

OK, let’s start with New Years and the 4th of July. New Years is Jan 1 and 4th of July is July 4, but sometimes those days will fall on the weekend, so I figured there’d be a rule for when to use the preceding Friday and when to use the following Monday.

Some follow rules I know, like Thanksgiving which is going to be whatever November Thursday falls between the 21st and the 28th, and Labor Day is the first Monday in Sept), those I didn’t need help with.

There are some I don’t know, like President’s Day and MLK Day. (actual date defined by hard date like 4th of July? or the xth some-weekday in monthname?)

And I know Good Friday if I know Easter but I forget what Easter is (something weird like the first Sunday after something else happens for the last time that year?)…

Anyway, so I call HR to ask what they use when making the holiday schedules out for the following years, and they said:

Hmmm…so what rule does the bloody calendar-manufacturing industry use?

All holidays have their own rule. (Note, this is for the U.S.) Some holidays are fixed dates (Independence Day); some fixed days within a month (Memorial Day, Labor Day, Thanksgiving); and some are based on other occurrences (Easter). Easter is a calculated holiday:

(from the Columbia Encyclopedia)

Several Christian holidays are calculated from the date of Easter.

My employer follows the same rule as the federal government for when a holiday falls on a weekend:

A great reference site is The Worldwide Holiday & Festival Site. You can find holidays by country and religion. Did you know that today is Sovereignty and Thanksgiving Day (Haiti) and Day of National Unity (Yemen)?

New Year’s Day January 1.
Martin Luther King’s Birthday Actual birthday is January 15, but the Federal Gov’t observes this holiday on the third Monday in January
President’s Day This is actually Washington’s Birthday. The actual birthday is Feb 22 (or Feb 11, old style). The Federal Gov’t observes this holiday on the third Monday in February.
Good Friday Good Friday is the Friday before Easter. Easter is celebrated on the first Sunday after the full moon that occurs on or next after the vernal equinox (fixed at March 21) and is therefore celebrated between March 22 and April 25 inclusive. This date was fixed by the Council of Nicaea in 325.
Memorial Day Last Monday in May
4th of July Known as Independence Day. Observed on July 4.
Labor Day Observed on the day my wife gave birth to our first child :D. Seriously, however, Labor Day is the first Monday in September. (My sister-in-law went into labor on Labor Day).
Columbus Day Second Monday in October
Thanksgiving Thanksgiving is observed on the fourth Thursday in November.

Zev Steinhardt

Here’s some more info. Since you didn’t specify which holidays your wanted the rules for, these are the federal holidays:

[ul][li]New Year’s Day (Jan. 1)[/li][li]Inauguration Day (Jan. 20)[/li][li]Martin Luther King, Jr. Day (3rd Monday of January)[/li][li]President’s Day (3rd Monday of February)[/li][li]Memorial Day (last Monday in May)[/li][li]Flag Day (June 14)[/li][li]Independence Day (July 4)[/li][li]Labor Day (first Monday in September)[/li][li]Columbus Day (second Monday in October)[/li][li]Veterans’ Day (Nov. 11)[/li][li]Thanksgiving (fourth Thursday in November)[/li][li]Christmas Day (Dec. 25)[/li][/ul]

Again, if the holiday falls on the weekend, the observed day is the Friday preceding or Monday following. The Worldwide Holidays site I linked to above gives the following information about Inauguration Day:

It’s a holiday that doesn’t affect most of us. Even the Post Office delivers mail on Inauguration Day (assuming it’s not on a Sunday).

The Worldwide Holidays site also list many non-holiday observances along with the rules for determining when they occur. For example, Mothers’ Day is the second Sunday in March, and Secretaries’ Day is Wednesday of the last full week of April, though apparently, it is now Administrative Professionals’ Day.

There are also links to individual states’ holidays.

Easter: “first Sunday after the first full moon after the equinox” is not QUITE right.

It’s the first sunday after the “Paschal Full Moon”, which is the first “Ecclesiastical Full Moon” after March 20. EFM’s are fixed approximations made centuries ago, and may be a couple days off from the actual astronomical full moon, although they weren’t bad approximations.

Excruciating detail may found here:

http://www.chariot.net.au/~gmarts/easter.htm

Thanks Jeff and Zev!

::goes off looking for a formula to calculate occurrences of the full moon::

A clarification: Easter (like the Chinese new year) falls on different days of our calendar but on the same day of the original calendar in which the day was marked. Easter (as passover) was originally marked on the Jewish calendar. Jewish festivities fall every year on the same date of their calendar (but differnt dates for us). Conversely, Christmas falls on the same day every year of our calendar but different dats of the jewisg calendar

Yet another clarification: Originally, Easter was tied to the Jewish Passover, but at some point the Church decided that it wasn’t worth keeping the whole Jewish calendar around just for the sake of calculating Easter, so they came up with the afore-mentioned formula, instead, which usually ends up with the same date.

What, they couldn’t just ask the nice Jewish family down the street when Passover was?

As far as the government of the United States is concerned, Easter is not a government holiday. Sunday, on the other hand, is one to the two weekly holidays–those being Saturday and Sunday.

Er, make that “one of the two”

Not to mention the eastern and western churches use different formulas to calculate easter. It is amazing how people will find reasons to quarrel if they set their minds to it.

Fascinating, this Easter thing!

Monty, it ain’t the government that I’m doing this for; it’s my employer, and they offer Good Friday as an annual holiday.

yabob, thanks for the link but I’m not working in VB and all the calcs at the link you provided are VB scripting rather than mathematical formulas.

I found several dozen sites that contained the following Easter-FAQ text which contains an incorrect Easter-calculation formula. e.g. –

http://www.kolumbus.fi/jimenez/ca_faq2.html

or

http://www.boulder.nist.gov/timefreq/general/calendars/calendar-christian-easter.html

or

http://www.tondering.dk/claus/cal/node3.html

The formula provided is annoyingly written (keeps redefining a variable as a variation on its previous defintion instead of giving it a new variable name) but the math seems to be straightforward…

Anyway, it calculates correctly for all the years I threw at it except for 2001. It yields 4/8/01 instead of 4/15/01 for the year 2001.

In the process of looking for a table providing me with correct dates for a range of years (to check the formula against), I found the following page

http://193.55.36.92/enicolas/computer/easter.html

which contains a formula (messier, and without a glimmer of explanation for why or how it works) that yields correct results for 2001 as well as all other dates I’ve tried.

So I’ve got it (and all the other holiday auto-calcs) working in FileMaker! Thanks, everybody, for your help!