If the IRS or State government questions your deductions or business losses, you may need a copy of your return to prove your return was accurate. However, there are limits to how far back the government can look.
The IRS recommends taxpayers keep their returns and any supporting documentation for three 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 six years back, or seven 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.