Atlanta homeowners rattled by skyrocketing tax estimates have been assured the figures were wrong, but despite the errors on assessment notices, the appeals clock is still ticking.

The deadline to challenge the Board of Assessors on appraised property values remains June 21 -- 45 days from May 7, the date on the notices, Fulton County Chief Appraiser Burt Manning said Wednesday.

Manning said the only thing wrong with the Atlanta notices is the dollar figure listed under "total estimate." Thousands of dollars were tacked on to estimated bills because of a computing mistake that added a commercial solid waste charge to most residences in the city.

Appraised home values, the figures that can be contested, were printed correctly, he said.

"There's nothing wrong with the assessments or the appraised values," Manning said.

The deadline, however, remains a source of trepidation. Taxpayers fear that if they trust that actual bills will go down, only to find out otherwise after they're mailed later this year, they'll have to pay up or face property liens.

The prospect worries Michael Johns, an Emory University ear, nose and throat surgeon who's having trouble sorting out the mess. The assessed value on his Buckhead home fell from $1.7 million to about $1.5 million, but his notice said his taxes would increase by about $1,000.

Johns said that unless Atlanta taxpayers can be assured they'll receive accurate bills, they shouldn't be held to June 21.

"The question is, are they going to get the right numbers out to people?" he said.

In a live Twitter chat Wednesday, Manning told residents that taxes and homestead exemptions should be accurate on actual bills. Appeals should be based on assessed values, not estimated taxes, Manning said. The notices included last year's homestead exemption, which increased this year from $25,000 to $30,000.

Kate Siegel, who took part in the TweetCast, said she'll be appealing the value of her Castleberry Hill loft, but not because of her inflated tax estimate. The loft sits empty, and while she's been unable to sell it for the $85,000 she paid for it in 1997, the assessors office has kept the value at $140,000.

"I'm bleeding left and right here," she said. "It's not so much the inefficiency that I'm annoyed with, it's the incompetence, and the fact that I've been dealing with this for the past 10 years."

Manning still couldn't say Wednesday who's to blame for the calculation error. Though still not indicating whether the mistake was made by the county or contractor Tyler Technologies Inc., which provided the software, Manning took responsibility.

"We do know enough to know that our staff could not have corrected this without help," Manning said, "but we also know that if we'd done a little bit more sampling, we probably would have picked that up."

Fulton County Information Technology Director Ryan Fernandes said he doubts Tyler is to blame. The company sold the county the software -- iasWorld -- in a 2009 contract for $355,000, according to the Purchasing Department.

Blaming Tyler for the error, Fernandes said, would be like blaming Microsoft for data entry mistakes in an Excel spreadsheet.

"If a formula error happened, that's more the responsibility of the user department," he said, referring to the assessors office.

Determining who committed the error will determine who will bear the cost of correcting it, if there is a cost.

Manning said sending out letters with corrected estimates would cost taxpayers about $50,000 to $60,000, not counting labor and overtime costs. In that case, the June 21 deadline would still apply.

If his office was to send out new assessment notices, which is unlikely, it would trigger a new 45-day deadline.

Sending tax assessment notices to every property owner in the county, along with estimated tax bills, was thrust on assessors offices by Senate Bill 346, which went into effect Jan. 1.

Senate Majority Leader Chip Rogers, R-Woodstock, the bill's sponsor, said he does not believe he asked too much from assessors offices, nor does he sympathize with Fulton.

"They've had a year to prepare," he said. "It's a math problem, and they've had an entire year to figure out the math problem."