Filing a tax return once is enough of a hassle. Doing an amended return for the same tax year—in other words, filing twice—seems like way too much. Yet millions of amended tax returns are filed by individual taxpayers each year.

Does an amended return increase your chance of being audited? Technically, no. But it will extend your exposure to IRS challenges. The agency can come after you for back taxes for up to three years from the date you file a return, and if you re-file, say, a year after the fact, that restarts the clock.

Still, filing an amended return can put money in your pocket. So here are some of the most common reasons to file IRS Form 1040X.

You get an amended 1099, K-1, or W-2. These are forms sent to you by banks, brokerages, investment partnerships, employers, or others. It’s not uncommon for these firms to make mistakes and resend a corrected form months after sending the original. And even if the corrected form will mean only a small change in your tax liability, you’ll still need to file an amended return, since the government also receives a copy of revised forms and will match them to your return.

You’re a sole proprietor, a shareholder in an S-Corporation, or the owner of a partnership. As such, you may have strong incentives to file an amended return, since pension or profit-sharing plans for one year can oftentimes be funded with earnings from the following year. Say you receive a windfall prior to the due date for filing your return (excluding extensions), but after you already filed. You can use that windfall to increase your retirement plan funding for the prior year, retroactively giving yourself a larger deduction. You can reflect the change on an amended return.

You discover an overlooked deduction when checking through your records, such as from a charitable contribution.

The law or IRS rules have changed. Sometimes the IRS clarifies a rule or a court ruling will liberalize a tax break.

You miscalculated when figuring your tax liability for selling a mutual fund. Often, investors count only their original purchase price as their cost, not realizing that reinvested income also qualifies. Your actual gain could be much lower than the amount you reported to the IRS.

In most cases, filing an amended return will not be expensive. And if only one or two calculations have to be changed, it shouldn’t be a big deal. No one likes to deal with the IRS and taxes, but you could be leaving money on the table by shunning a 1040X.

To keep up-to-date on tax law changes affecting your taxes and your business, visit www.irs.gov or call 800 829-1040 (individuals) or 800 829-4933 (businesses).