How far back can the IRS audit you? Here's what might trigger one.

It's rare IRS agents will come knocking on your door to perform an audit these days. Most audits are now done via mail or in person at an IRS office or the taxpayer's place of business, but they're scary, nevertheless.

When you're audited, it means your return was selected from a batch of returns for a closer inspection.This happens because your tax filing was among those that showed the "highest potential noncompliance," the IRS says. The agency uses data driven algorithms, third-party information, whistleblowers and information you provide to determine if income, expenses and credits are reported accurately.

The easiest way to avoid an audit is to be "accurate, honest, and modest," said Eric Scaringe, principal at certified public accounting firm UHY.

What triggers an IRS audit?

Mismatches. "One thing tax jurisdictions like more than money is information," Scaringe said.  "They look for mismatches, and use AI (artificial intelligence) tools to find it and send autogenerated notices. That's low hanging fruit."

For instance, make sure you enter your information from your W-2 income tax form correctly so it's consistent with the income that's stated on official income tax documents like a 1099 or W-2, said Erin Collins, National Taxpayer Advocate at the Taxpayer Advocate Service division of the IRS. Or else, you can expect an IRS inquiry.

"We find a lot of taxpayers take their last paystub (of the year) and use that number," she said. But they can run into problems because that last paystub may not cover their typical pay period.

She also recommends parents discuss who will be claiming a child on their return if they file separate returns. They should also ensure additional caretakers like grandparents don't try to claim a child on their return if they don't meet the IRS' requirements for doing so. Otherwise, an audit may be triggered if multiple people try to claim the same child as a dependent on their returns.

People often get tripped up on the earned income tax credit (EITC) because IRS records show that a child claimed by the taxpayer does not meet the relationship or residency test to be considered a qualifying child, according to the Taxpayer Advocate, an independent organization within the IRS that works for taxpayers.

Michael Steffany, a senior tax attorney at Withersworldwide, said in his experience, "the IRS concentrates its efforts on those items most likely to result in a large amount of additional tax due."

"We continue to see high net worth taxpayers, as well as taxpayers with non-U.S. income and foreign entities, be a particular point of concentration," he added.