Amidst the fight over tax dollars for mass transit in the Chicago region, here is a breakdown of where the tax money comes from and who gets to spend it:

Metra, the CTA and Pace receive around half of their operating revenues from fares, but most of the remainder comes from sales taxes. It’s calculated using unbelievably complicated state formulas that incorporate geography into divvying up the spoils. However, a 2008 state law change raising the sales tax left the disposal of some of the money up to the Regional Transportation Authority. That’s meant power struggles the last two years.

A look at 2012 sales tax dollars received by the RTA shows that 27.5 percent of that revenue derives from Chicago. The biggest chunk, or 50 percent, comes from suburban Cook County. Elsewhere, DuPage County contributed 8.6 percent, Lake 5 percent, Will about 4 percent, Kane about 3 percent and McHenry not quite 2 percent.

There are two different ways to interpret those numbers. Cook County, including Chicago, delivers 77 percent of transit funding. Or — the suburbs combined provide 72 percent of transit funding compared to Chicago.

In terms of revenue going out in 2014, the CTA will get $661 million in operating funds from the RTA, Metra receives $365.4 million, and Pace $151.6 million. When you cut up that pie, it’s 56 percent CTA, 31 percent Metra and 13 percent Pace.

So it sounds like complaints from DuPage County about the money they are contributing is a smaller slice of the pie overall – it is suburban Cook County that is chipping in the most.

Another issue: suburbanites might complain that they are not getting in return the money they put in but isn’t more expensive to run good mass transit in the spread-out suburbs? In other words, if the collar counties wanted mass transit similar to that of Chicago, wouldn’t it cost more from everyone?