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With tax season coming to a close—the filing deadline is April 18 for most Americans this year—you've probably finished your return (if not, do this), and you're hoping that a fat refund check is the only memento you'll have of the 2015 tax season.

But if you're worrying about a different kind of reminder, relax. A very small number of taxpayers end up facing a dreaded IRS audit.

Last year, the IRS audited fewer than 1% of all taxpayers—0.84%. That's the lowest level in more than a decade and the third consecutive year of audit rates below 1%. And the trend doesn't seem likely to reverse this year.

While your overall odds are low, you may have a few items lurking in your return that could increase your risk of becoming the target of an audit.

The IRS doesn’t explain exactly why its auditors single out some returns for extra scrutiny, but a look at the agency's track record provides some clues as to which groups draw the most attention. Specifically, these nine things could land you a conversation with the IRS.

1. You Earned More than a Million

Once you report income in the seven digits, you're chances of being audited skyrockets to 8.42%, far above the overall rate of 0.84%. And those with $10 million or more in income should be on standby for a double check from the IRS—more than a third of those returns are audited.

Due to budget cuts over the past few years, the IRS has been targeting the rich in an effort to "work smarter." The idea is to look more closely at those with the most money (and the most the to hide) in order to net the best return on an audit investment.

Here's the full breakdown for 2015:

Returns by Income Percent of total returns Percent audited in 2015
All returns 100% 0.84%
No adjusted gross income 1.76% 3.78%
$1 – $24,999 38.51% 1.01%
$25,000 – $49,999 23.23% 0.50%
$50,000 – $74,999 13.13% 0.47%
$75,000 – $99,999 8.42% 0.49%
$100,000 – $199,999 11.15% 0.64%
$200,000 – $499,999 3.08% 1.54%
$500,000 – $1 million 0.48% 3.81%
$1 million – $5 million 0.21% 8.42%
$5 million – $10 million 0.01% 19.44%
Over $10 million 0.01% 34.69%

Source: Internal Revenue Service Data Book, 2015

2. You Took Really Big Charitable Deductions

Giving to charities can be a great tax write-off, but if your donations are disproportionately large compared to your income, expect the IRS to ask to verify your altruism, says CPA Cari Weston, director of taxation for the American Institute of CPAs.

Why? The IRS tracks the average charitable contribution for folks at every income level. Donations that exceed the IRS's expected amount are seen as suspicious. But if you've actually been that generous, fear not. Just keep detailed records of your giving, including receipts for all contributions of cash and property.

Failing to get an appraisal for a donation of valuable property, or forgetting or incorrectly filing a Form 8283 for non-cash donations greater than $500, puts an even bigger audit bull’s-eye on your back. And the mistake could lose you the entire deduction, even if you're entitled to it, warns Bill Smith, managing director for CBIZ MHM’s National Tax Office.

"Anything that you don't have to substantiate when filing, anything that the IRS knows it is easy for you to make up a value for, gets extra attention, and charitable contributions is a big example of this," says Weston.

3. You Filed an Estate Tax Return

While estate tax returns are rare—the IRS only received 35,619 in 2015—the agency very carefully rakes over these forms. Overall, 7.8% of these returns received extra scrutiny last year.

And much like with higher income returns, the bigger the estate the greater the odds it'll be flagged for an audit. More than 16% of estate returns with assets between $5 million and $10 million were examined, and 31% of returns with assets exceeding $10 million were audited.

4. You Failed to Report All Your Income

Any company you work for is required to send the IRS copies of all 1099s and W-2 forms you receive. If the income you report doesn't line up with those forms, that mismatch will trigger at least a letter audit.

If you have multiple sources of income, say you freelance, it can become hard to keep track of all the income year earned, and the more likely you are to leave out a payment. To avoid missing a 1099— because it was mailed to an old address, say—keep track of all work you complete and the agreed payment. Not getting a form is not an excuse for not reporting the income.

Receive a form listing incorrect income? Get the issuer to file a corrected version with the IRS.

5. You Took Losses on Rental Properties

The IRS has really strict rules for who can claim rental losses, and most people can't make the case for taking them, says Weston.

That's because you can deduct rental real estate losses on your taxes only if you actively participate in the renting of your property or are a real estate professional. If you rent your own spaces, you can deduct up to $25,000 of losses against your other income. This perk phases out as your income tops $100,000 and disappears entirely for those earning $150,000 or more.

Developers, brokers, landlords, and other real estate professionals who spend more than 50% of their working hours and over 750 hours each year "materially participating" in real estate can write off all losses without any income restrictions.

Naturally deductions that have no limits are ripe for abuse, so the IRS actively scrutinizes those who claim rental losses, in particular any taxpayer claiming to be a real estate professional. The agency will check your return against your W-2 forms and business returns, and verify that you worked the necessary hours in 2015 to ensure you're actually entitled to that tax break.

6. You Wrote Off Alimony Payments

Alimony payments are deductible for the payer and taxable for the recipient, if certain conditions are met. To get the tax break, payments must be made under a written separation agreement or divorce or separate maintenance decree. The document cannot say the payment isn't alimony. And liability for the payment ends with the paying spouse's death. Divorce degrees that don't meet these requirements won't satisfy the IRS.

Alimony also doesn't include child support or noncash property settlements. The IRS knows people get confused about these rules and take write-offs that don’t satisfy the agency's requirements. The IRS also likes to give these claims another glance to be sure both the payer and recipient properly reported the alimony on their returns. Any mismatch between exes will trigger an audit for both.

7. You Broke the Rules on Foreign Accounts

If you've got money stashed away in accounts overseas, be sure to carefully report those assets to the IRS, says Smith. Failing to do so can lead to severe penalties, in addition to an audit.

You need to file a FinCEN Form 114 by June 30 to report any foreign accounts that contained more than $10,000 at any point last year. If you hold assets topping $50,000 overseas, you'll need to attach Form 8938 to your return. International banks are required to identify American asset holders and provide information to the IRS, so don't think you can escape paying up by stashing funds in the Cayman Islands.

Since 2011, when the IRS introduced offshore tax evasion initiatives, the agency has been cracking down on international returns. In 2015, 4.3% of international returns were audited.

“We view offshore tax evasion as an issue of fundamental fairness. Wealthy people who unlawfully hide their money offshore aren’t paying the taxes they owe, while schoolteachers, firefighters and other ordinary citizens who play by the rules are forced to pick up the slack and foot the bill," then- IRS Commissioner Douglas Shulman told the American Institute of Certified Public Accountants in 2012.

8. You Claimed Big Deductions for Your Business

Taking business deductions that seem disproportionately large compared with your income is an invitation to the IRS to investigate, says Weston. Same goes for reporting an operating loss for your business. If you've got the proper documentation for the write-off, go for it, but know that you may be called upon to back up your story.

The IRS knows that certain tax deductions are abused frequently. People claim a computer and desk as a home office deduction, family vacations as "business travel," or 100% business use of a vehicle, which the IRS knows is very unlikely to be true. People like to get creative with the deductions they try to claim, says Smith, but such thinking, or cheating as the IRS would say, can backfire.

Filing a Schedule C to claim business income and expenses triples your odds of being audited. Not surprising when you consider that Schedule C filers are estimated to report only 57% of their income, totaling roughly $68 billion in unpaid taxes each year, according to Barron's.

"If you work for an employer and have a W-2, there is a third party confirming your income," says Weston. "There is no room for guessing. When you're self-employed, you're the only one reporting to the IRS. You're expected to report all income, but the IRS knows sole-business owners or owners of pass-through entities like S-corporations are likely to hide some earnings or abuse deductions because of the high crossover between business and personal use."

9. You Took an Early Payout from a Retirement Account

The IRS is paying special attention to owners of traditional IRAs, 401(k)s, and other workplace retirement plans who withdraw sums from their accounts before age 59 1/2. That's because those distributions are subject to a 10% penalty in addition to regular income tax.

Withdrawals can escape this penalty if made for certain reasons, such as payouts used to cover large medical costs or the total and permanent disability of the account owner. A full list can be found on the IRS website.

Studies conducted by the IRS and the Government Accountability Office have found that the complex tax laws surrounding retirement distributions often confuse taxpayers, leading many individuals to make errors on their returns. One of the most common mistakes: claiming an exception to the 10% penalty when you don't actually qualify.