Short Count

Though the ancient Maya had been using the Period Ending version of the Long Count they eventually shortened it further by the Postclassic period. This even shorter version does not count a group of katuns like Period-Ending. The Short Count -- whose dates are called katun-ending dates -- only stated the date a katun ended and used a very simplified version of the Tzolkin. This second version was a cycle that didn’t repeat until 256.25 years had passed.

Setup
Instead of the regular way of counting the Tzolkin, days were counted using the numbers 1 through 13. Each day had the name Ahau, and was paired with a number between 1 through 13. But it wasn’t just a simple matter of successively counting higher to 13 and starting over. Each day skipped two numbers in the sequence.

An example of the way the Short Count’s dates are written goes like this: katun 13 Ahau. The next katun would be written katun 11 Ahau, after that would be katun 9 Ahau and so on. Once you get to katun 1 Ahau you count down two to get katun 12 Ahau, then 10 Ahau, et cetera.

Consideration
The Short Count is the kind of time keeping that the authors of books like the Chilam Balam used. In these books, the katun date would be recorded in the u cahlay katunob or the “count of the katuns”. Katuns were named after the last day that they fell on.


References:

“The Ancient Maya”; Robert J. Sharer, Loa P. Traxler; 2006

Period Ending

As time passed and the ancient Maya civilization declined, the Long Count became less used in its full form. Instead a shorter form known as Period-Ending began to be used.

Setup
The ancient Maya used the Period-Ending version of the Long Count at least since around the Late Classic period. Period-ending dates counted katuns and the day the katuns ended on. Period-ending dates still used both calendars of the Calendar Round. The period-ending dates form a cycle that does not repeat for around 19,000 years.

An example of the period-ending date format goes like this. If it was the 8th katun and it ended on 4 Ahau 13 Cumku, then it would be written katun 8 4 Ahau 13 Cumku.

Consideration
The Period-Ending version was itself eventually replaced by an even shorter version of counting katuns. This second version is called the Short Count.

References:

“The Ancient Maya”; Robert J. Sharer, Loa P. Traxler; 2006