Are you serious?

Yes.

What’s wrong with the Gregorian Calendar?

See SAC13 vs Gregorian Calendar.

Do you really think this calendar will ever be adopted?

No. Maybe. I don’t know. I think this is the best calendar reform proposal we have so far, not because I’m arrogant, but because if I had seen a better one, I wouldn’t have written my own. Practically all other proposals I saw have some serious issues, lack detail and depth, and don’t have official - and open - reference implementations.

The only notable exception is Symmetry454; to say that it is well-thought-out would be an understatement. Sadly I don’t agree with the leap week decision and the twelve month layout. You can find a detailed comparison between SAC13 and other calendars (including Sym454) here. I think the biggest reason why there probably won’t ever be a calendar reform (with the exception of Gregorian Leap Year Rules changes) is the cost and effort, and the fact that we have bigger issues.

What happens to birthdays, wedding days and anniversaries?

It depends on what you mean by “day”. Technically, your birthday will always be on the same day, no matter which calendar. However, the way we write or refer to that day differs between calendars, including SAC13. More about that here. You can also check out the calculator if you want to know how your birthday is written in SAC13.

How long will the leap year rule be accurate?

See leap years.

Why does the year start with a letter?

See Millennium Indicator.

What if we need years before A000 or after Z999?

See SAC13 limits.

You didn’t invent 13-month calendars!

First, that’s not a question 🙃. Second: I know, and I never claimed that. I looked at many 13-month calendar proposals and practically all of them have major flaws. Comparison to other calendars.

Why 13 months?

See Why 13 months.

Why “Addenduary”?

I somehow really like the month name “Addenduary”. It combines “addendum” with the suffix “-uary” and, to my surprise, has (at the time of writing this) zero results on Google¹; so in my opinion, it’s a perfect candidate for a name for a new calendar month. The only downside I see is that the name is quite long, one letter more than September.

“Sol” from IFC would be shorter but it can only ever be accurate for one hemisphere. I also looked at month names from other calendar proposals like Nova, Extra, and Xtra, and tried to come up with more novel ones, but I still think Addenduary sounds great.

Why seven days per week?

See why seven day weeks?

Why start the new year with the March equinox?

It was used as a reference point throughout history for different things, including many calendars, and from various cultures. This is still true in modern astronomy, and the northward equinox (March equinox) is used in definitions as a reference point in different coordinate systems, etc. It seemed like a natural choice to use it as the starting point for the year.

Why positions sync days at Addenduary and August?

Again, it felt like a natural choice to add the Year Day in Addenduary. This results in a long weekend at the end or beginning of the year, to allow for celebrations that typically happen around New Year’s Day. For the Leap Day, I wanted it to be roughly in the middle to spread them out evenly, but there is no middle with thirteen months. August was chosen because it’s the last month that is entirely in the first half of the year, so when comparing years, months, quarters, and weeks, there is never a difference greater than a single day.

How does SAC13 compare to other proposals?

See SAC13 vs others.

Why add 10’000 to the years?

The calendar aims to unite people from different cultures, groups, and religions. Beginning the calendar roughly around the time humans started with agriculture and thus made a big step in the direction that led us to where we are today seems like a reasonable thing to do. There is a great video from Kurzgesagt about that (here) and also other good points for it here on Wikipedia.

Why are negative years not officially supported?

See SAC13 years.

Tell me more

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