How long to keep your tax documents / If you have ever lived in fear of the IRS auditing your tax return, here's some advice on how to protect yourself.

David John Marotta for USA Today writes: You likely live in fear of a tax audit. Here's how to protect yourself.

If the Internal Revenue Service suspects you underreported your gross income by 25% or more, it can challenge your return for up to six years. If the IRS suspects you filed a fraudulent return, no statute of limitations applies.

When the IRS challenges your return, the burden of evidence verifying your claims rests entirely with you.

If you haven't been traumatized by an audit, you probably keep little of your financial documentation. If you have, you're probably terrified to part with a single receipt. The IRS is one of the few courts where failure to produce proof of your claims results in the assumption that you stand guilty.

Save all financial documents used to create your tax return.

Retain a paper copy or receipt of any tax-relevant financial exchange. Scan these documents and archive them electronically or acquire them in an electronic format.

If your purchase came with a manual or warranty, store all documents in the same electronic and physical location. If the purchase constituted a business or other deductible expense, record the expense and why it justifies the deduction. Store this information with the receipts.

The IRS also regards bank or credit card records as insufficient documentation. Keep statements just long enough to reconcile your account.

Keep brokerage statements indefinitely for taxable accounts.

You must report the cost basis, or original value, of any security you sell to calculate the capital gains tax.

For a mutual fund with 30 years of reinvested dividends, each dividend payment is part of the cost basis. As a result, sometimes you can compute the cost basis only if you access the complete transaction history.

Without knowing the cost basis, the IRS could treat the entire value of the investment as gain.

If you lost the record of how much you originally paid for an investment, instead of selling and paying 15% or more of the value in taxes you can use that investment as part of your charitable giving.

Gifting appreciated stock avoids the tax and still qualifies for a full deduction. The IRS still asks for the original purchase date and price for gifted securities, but leaving these blank doesn't affect your tax owed.

Many custodians keep several years of electronic copies of brokerage statements and must send any known cost basis when you transfer to a new custodian. If your current custodian has the correct cost basis of your securities, you probably no longer need to keep brokerage statements. Better safe than sorry with the IRS, though.

Permanently keep records of nondeductible contributions to your individual retirement account.

You may need the records every year in your retirement that you withdraw money to show that a portion of the withdrawal is not tax deductible. To avoid the hassle, clear out nondeductible IRA contributions by converting all of your IRAs to Roth accounts.

Keep partnership documents, contracts and commission or royalty structures forever.

This includes property records, deeds and titles, especially those relating to intellectual property. It also includes transfers of value for estate planning.

Save all your tax returns.

After you file, save the paper or electronic copies, or both, with the rest of that year's documents.

Once a year, scan and compile the records into PDFs and send them electronically to the certified public accountant who does your taxes. Scanning the information gives you an electronic backup of the paper indefinitely.

Keep returns and all supporting documentation at least seven years. The IRS can audit your return for up to three years from your filing date, a limit applying only to good-faith errors.

David John Marotta, CFP, AIF, is president of Marotta Wealth Management of Charlottesville, Va.