On thing that Accounting firms do is file amended tax returns, but we don’t always do it right away. One of the first things that we look at is whether or not it’s worth it. Sometimes making adjustments aren’t worth the cost of refiling (especially if you’re paying an accounting firm to do it for you).
If you’re considering doing it for yourself, ask yourself if your time is worth filing the 1040X out, because it can be pretty complex. If it is, make sure that you’re doing it correctly, because the IRS may not agree with the changes and decide to audit you. Filing the 1040X also resets the three-year audit clock that the IRS has to audit you, so there’s that too.
The other thing to keep in mind is that if it’s a long term error, like not including some sort of business paid interest over the space of a few years, you may be filing several years of amended returns. You have to keep all of that paperwork straight to amend the correct return.
You’ve probably seen this one coming from a mile away, but if the amounts are big enough, you should seriously think about hiring an accounting firm to do this for you, and to keep the paperwork in order. We do it, so do other CPAs, so try to find one in your area to check their rates (you may need to meet them though, because different kinds of engagements have different rates).