Talk:Doomsday rule

The Year's First Sunday method adds further simplification to the odd+11 method, making the algorithm truly simple -- memorizable in one sitting.

https://firstsundaydoomsday.blogspot.com/2011/01/learn-by-example.html Jbaber (talk) 04:02, 25 January 2023 (UTC) Reply

I've memorised and practised a few variants of the Doomsday rule, and I must say this one is really the most efficient one I've seen. Lets me compute the day of the week within a few seconds even after moderate practice. SchnitteUK (talk) 15:13, 24 December 2025 (UTC) Reply

Why is there the section "Anchor days for some contemporary years"? It’s Doomsday (itself!) of those years.

A couple of years ago, the section was named Doomsdays for some contemporary years... Then someone changed it and it makes no sense. The anchor days (of a century) are those you use to count the DOOMSDAY of the year! E.g. anchor day of 2000-2099 is Tuesday ... and Doomsday of 2022 was Monday. Hopefully you understand what I mean. 85.237.234.127 (talk) 19:25, 13 March 2023 (UTC) Reply

While the text of this article makes it clear that the non-existence of a February 29, 2100 will not derail the computations, please include some examples from a year later than 2100 to show that this is so and enable readers to follow the calculations through years such as 2100, 2200, and 2300 that won't be leap-years even though 2000 was and 2400 will be.2600:1700:6759:B000:1031:6B84:3136:E1F7 (talk) 09:15, 6 August 2023 (UTC)Christopher Lawrence SimpsonReply

Frankly, I think there are allready way too many examples, too long tables, etc., in the article, obscuring the simplicity of the Doomsday method. Nø (talk) 14:55, 6 August 2023 (UTC) Reply

It just loops over in a 400-year cycle. The 2100s are identical to the 1700s, the 2200s are identical to the 1800s, and so on. The 2500s and 2900s will be like the 1700s and 2100s again. The caveat to this is that the Gregorian calendar still has an error of about one day in 3,000 years, so it might be that around the year 4500 there will be a need for another calendar reform to modify the lear year rule. When that happens, the Doomsday rule will need to be adjusted. But until then, you can use the 400-year cycle to compute weekdays even for the distant future. SchnitteUK (talk) 15:19, 24 December 2025 (UTC) Reply

I can't find this anywhere in the article, nor on the disambiguation page for the term. It's possible it's buried in here somewhere, but even if it is, it ought to be clarified at the top. Being able to calculate a doomsday doesn't make sense when you don't know what a doomsday is. The header does link to Determination of the day of the week, which has a section called "The 'doomsday'", but that just says "This is an artefact of recreational mathematics. See doomsday rule for an explanation." The reader is led back where they started. Moonreach (talk) 15:23, 12 May 2025 (UTC) Reply

First paragaph:

Doomsday for the current year in the Gregorian calendar (2025) is Friday. Simple methods for finding the doomsday of a year exist.

Perhaps better linkage to the explanation regarding what the series of a year's doomsdays represents is needed (i.e. Doomsday this year is Friday, therefore the dates ( 4/4, 5/9, 6/6, etc) are also Friday). DarkStarHarry (talk) 15:31, 12 May 2025 (UTC) Reply

That doesn't tell me what a doomsday is, though. I swear I'm not being deliberately obtuse. It's not the first day of the year, which is a Wednesday for 2025, so where does it come from? Moonreach (talk) 15:35, 12 May 2025 (UTC) Reply

Correct, the first day of a year is always Doomsday minus 2 (1st Doomsday of a year is January 3rd).

Doomsday is named after the Doomsday formula to determine the day of the week. DarkStarHarry (talk) 15:40, 12 May 2025 (UTC) Reply

I finally get it, although I had to consult this and then reread the header again. The doomsday is the shared day of the week which occurs on the last day of February, 4/4, 6/6, 8/8, 10/10 and 12/12 for any given year. That information was already in the header, but not in a way I could parse when my question was "What is a doomsday?" because the wording doesn't emphasize the doomsday itself, just the structure around it. Thanks for helping. Moonreach (talk) 15:51, 12 May 2025 (UTC) Reply

I hope we can pin this question as the unofficial TL;DR of the page. Cheers. DarkStarHarry (talk) 19:14, 12 May 2025 (UTC) Reply

The formula for correspondence with the dominical letter of the current year is wrong. It gives the correct result 'E' for 2025 (Jan 5, 2025 was a Sunday), but the (automatically calculated) formula ("A + 3") which is displayed is nonsense. I lack the skills to edit the complicated expression which calculates the formula, so maybe someone else could change it. Gzim75 (talk) 11:55, 17 September 2025 (UTC) Reply

I'm going to delete that last sentence with its complicated formulas. It goes beyond the exemption for basic calculation and is therefore a form of WP:Original research that's not allowed. Wikimedia's #expr does not lend itself to readability when the calculations get this involved, and this is unreadable and undebuggable. I doubt that even the original author could understand it easily if it's been more than a few months since they wrote it. Indefatigable (talk) 21:41, 17 September 2025 (UTC) Reply