Prince George's County is expecting to receive an additional $12.5 million after a successful bid to change the way the state accounts for county wealth.

County officials have long railed against the formula Maryland uses to determine how it hands out funding. In past years, the state would take a snapshot of residents' income tax returns on Sept. 15, called net taxable income, and base its aid off that finding.

Taxpayers can file for an extension until Oct. 15, however -- a step often taken by wealthier residents. Since these taxpayers are left out of the calculation, the complaint was, richer counties like Montgomery seemed more in line with Prince George's, where the vast majority of taxpayers files on time.

"It's gonna rectify this issue that's been around for quite a bit," said Brad Frome, deputy chief of staff to County Executive Rushern Baker. "Monetarily it'll mean $12.5 million more for education after the full five-year ramp-up."

The extra funding will rise in $2.5 million increments starting this fiscal year. Frome said the final schools budget will include the extra funding. The $12.5 million figure isn't set in stone, though — it could change depending on the state of residents' tax returns, though officials said it shouldn't vary wildly. Baker's office had originally estimated the net gain at $20 million.

The measure didn't pass without compromise, though. Montgomery County lawmakers were especially unhappy with delaying the state government's snapshot of their taxpayers, since it would likely lessen the amount of funding heading their way.

About 6.4 percent of Montgomery residents filed their income tax returns after the snapshot, compared with 2.7 percent of Prince George's taxpayers, according to the state comptroller's office.

State lawmakers struck a deal — while Prince George's and other counties with fewer late filers would get their snapshot delayed until October, Montgomery and some of the other wealthier counties are still going to be assessed in September.

"It's going to take five years for us to take the full amount we're entitled to," said Del. Jolene Ivey, chairwoman of the Prince George's County House Delegation. "Montgomery County will continue to get money that they're not entitled to."

Ivey still considers the law a victory. County representatives have pushed for such a change for years, including a provision buried in last year's ill-fated gambling expansion bill.

"It means more money for education funding," Ivey said. "I'm just glad that it finally happened."