To be safe, keep your income tax returns indefinitely, since they can be your paper trail on the valuation of basis of assets that are subsequently sold. Old supporting documents (receipts, canceled checks, credit cards, and so forth) should be kept six years. That’s because the IRS can go back three years from the filing date to audit your records and return and impose additional tax. In some cases, the IRS can audit up to six years after filing if income is underreported by 25% or more or if there is suspected fraud.