Some sources say three years — which is the maximum number of years the IRS has for auditing your tax returns under general circumstances. Most CPAs and tax attorneys will tell you that you should keep your tax returns for at least seven years, and that is the better advice. The IRS can reach back six years if they determine your income has been underreported by more than 25%. Even if you didn’t, you have to be ready in case the IRS thinks you did.