An error in calculating property tax exemptions will likely delay Fulton County tax bills, which normally go out in July. The late mailing will cause a domino effect that could require the county to borrow money to cover its debts.

If the tax bills are delayed "only a few weeks," Fulton will be fine, said Sharon Whitmore, the county's chief financial officer. But if the issue persists, it could mean payments come in later than anticipated. That could force the county to borrow money or dip into savings to pay bills that taxes were intended to cover.

The 2016 collections are used to pay off money that was already spent this year.

"I'm certain the Tax Commissioner will do everything possible to stay within our normal billing schedule and due dates," Whitmore said in an email Tuesday.

The error, caused by a vendor used by the tax assessor's office, kept Fulton County commissioners from setting the millage rate, which determines how property owners are taxed. If leaders don't know the tax rate, they can't tell residents how much they owe. The vendor, Tyler Technologies, has been working to correct the issue. Johns Creek first noticed the problem in June.

Commissioners had already delayed a vote to approve the millage rate by three weeks, as they waited for the problem to be resolved. Thursday they approved a rate that would be no higher than the current level of 10.5 mills.

The “roll-back rate” — expected to be between 10.412 and 10.5 mills — was approved without an actual number in an effort to keep the tax bills on time.

Daniel Jones, owner of the property tax appeals company Fair Assessments, said he couldn’t recall a situation like this.

“It could cause problems,” he said. “I don’t know for certain what earthquake might happen.”

The mathematical error that caused the delay, which nearly led to unnecessary and unintended tax increases for Fulton residents, was supposed to be fixed in June.

The problem stems from the way in which property tax exemptions — tax breaks given to those whose homes are their primary residences, and others —were calculated. In Fulton County and its cities, the exemptions were too high. The error meant cities and the county could have inadvertently taxed residents more than they needed to by failing to roll back the rate.

Georgia law requires governments to decrease the millage rate as values rise, or to advertise that they are increasing taxes if values rise and the millage rate stays the same.

In order for the process to stay on track, commissioners must have advertised the new millage rate this week. But the problem was not fixed in time for the commissioners’ July 20 meeting.

“The truth is, I don’t have the answer yet,” David Fitzgibbon, chief appraiser for the Fulton County Board of Assessors, said Thursday as commissioners peppered him about when he would know the true numbers.