The IRS recommends taxpayers keep their returns and any supporting documentation for 3 years after the date of filing; after that, the statute of limitations for an IRS audit expires.
If you've under-reported income by 25 percent , however, the IRS can go 6 years back, or 7, if you claim a loss for bad debt or worthless securities.
If you don't file, or if you file a fraudulent return, the IRS has no statute of limitations; so it may be best to keep your records indefinitely.
State documentation requirements
If you're paying state income taxes, the time you need to keep records will vary, depending on the particular state's laws.
Please see the following TurboTax guide, "How Long Do Federal and State Tax Returns Need to Be Kept?":