You’re not really in the clear until three years after the return is due, in most cases. So, that’s the statute of limitations that the IRS has. They have three years to assess you once you file the return to come back and say, “Hey, we think you made a mistake here.” Or, “We want to audit this line item that doesn’t seem to make sense.”
Now, typically these reviews by the IRS cover some minor numerical errors on the return. Maybe you put it some incorrect numbers or some different numbers than the information they have on hand. Perhaps you omitted a W-2 or 1099. In these cases, the IRS may send you a letter within a few months saying, “Hey we think you missed this. We’re going to add it on unless you have evidence for why it shouldn’t be added on.” In those instances, it happens pretty quickly. If however, you understate your income by more than 25 percent they actually have six years to come at you and say, “Hey we think you missed this,” and you’d probably be subject to a substantial penalty.