Imagine if we had this simple calendar with 13 months, and each of 'em was just 28 days long.

That means we'd have 364 days in a year plus one wildcard.
And every month would be exactly the same length.
Every month would have exactly 4 weeks.
Every 1st day would be Monday and every 12th day would be Friday and so on.
No more fussing over those odd months with varying days!
The days of the week would stay the same all year round, making it super simple to plan and organize stuff.

But what do we do with leap years

You know, those extras that don't quite fit into 364 days? And we'd also need to figure out how to match up with the solar year. It would be , for example, a Holiday- day off. Or something like that.
And from time to time we'd have two days off, because solar year is a little bit longer than 365 days.
And thats it. So simple so cool. Not my idea, but I really dig it.

Oh, another thing: It would be 13th zodiac sign. It exist already, and I's called
Ophiuchus

https://en.wikipedia.org/wiki/Ophiuchus