Because they are counting the DIFFERENCE.
It needs to be INCLUSIVE.
People do it all the time when they are doing dates.
They take the DIFFERENCE between the two days. For some applications that is ‘OK’, BUT not when you are counting something like a SHUTDOWN.
You have to INCLUDE Day 1, in this case, Saturday, December 22, 2018.
My calendar above shows it clearly.
But, try a simple example. Shutdown started Dec. 22. So, how many days shutdown at the end of Dec. 24. It is 3-days, NOT 2.
I actually saw Anderson Cooper talking about the shutdown being in its 13th day, above the CNN clock that said ’12’!