Fulton County property values will increase starkly this year — in part because the county neglected to keep up with rising valuations as the economy improved.

Most residents will see double-digit percentage value increases when letters detailing individual tax assessments go out next Friday. The median increase in value is 13 percent, according to preliminary numbers, but values in some neighborhoods rose as much as 79 percent. Of Fulton’s more than 2,300 neighborhoods, residents in 99 — or about 4 percent — could see their property values increase by 50 percent or more.

The jump in values doesn’t mean that property taxes will rise at the same rate.

Fulton County, school boards and cities each set their own millage rates, based on the value of the county's tax digest and their budgetary needs. State law requires that taxing entities hold public hearings before they set millage rates that would mean an increase in property taxes for the average person, even if the rate itself is unchanged.

Additionally, residents may be eligible for exemptions.

Still, many residents are likely to experience higher tax bills, even if millage rates fall. It’s just too soon to say how much.

Steve Pruitt, the former Gwinnett County chief appraiser who is consulting for the Fulton Board of Assessors, called the extent of the increase in property values a "drastic step." He said because Fulton didn't maintain regular increases, the county "had to play catch up."

“If the county would have kept up with those increase on an annual basis, then we wouldn’t be in this situation,” Pruitt said.

County assessments are required to be between 90 percent and 110 percent of fair market value. If assessments are outside that range, the state Department of Revenue can fine the county, Pruitt said.

Last year, Fulton's assessments came to 85 percent of fair market value, Fulton Chief Appraiser Dwight Robinson said. The Department of Revenue is investigating the county's appraisal and assessment practices, at Fulton's request.

Tax bills were delayed by two months last year.

Robinson said he did not know why Fulton had not kept up with rising property values. Last year, there were no updates to residential values. In previous years, they were incomplete.

The high increases can be seen from Chattahoochee Hills to Milton, including some in hot Atlanta neighborhoods like the Old Fourth Ward.

For those frustrated by the spikes, Robinson asked them to consider whether they might be able to sell their homes at the new values. If so, he said, they are fair.

“The bottom line is I think we’ve done a really good job of bringing values up to where they ought to be,” he said.