If you discover that you forgot something on your tax return, you can amend that return after it has been filed. The need to amend can include a number of issues:

Receiving an unexpected or amended K-1 from a trust, estate, partnership, or S-corporation.
Overlooking an item of income or receiving a late or corrected 1099.
Forgetting about a deductible expense.
Forgetting about an expense that would qualify for a tax credit.

These are among the many reasons individuals need to amend their returns, whether it is for the just-filed 2021 return or prior year returns.

Here are some key points when considering whether to file an amended federal (Form 1040X) or state income tax return.

1. If you are amending for a refund, you should be aware that refunds generally won’t be paid for returns if the three-year statute of limitations from the filing due date has expired. For example, the statute of limitations for the 2021 return will generally expire on the April filing due date for 2025. Some states have a longer statute.

2. Generally, you do not need to file an amended return to correct math errors. The IRS or state agency will automatically make those corrections. Also, do not file an amended return because you forgot to attach tax forms such as W-2s or schedules. The IRS or state agency will send a request asking for the missing forms.

3. If you are filing to claim an additional refund, we should wait until you have received your original refund before filing Form 1040X.

4. If you owe additional tax, file Form 1040X and pay the tax as soon as possible to limit interest and penalty charges that could accrue on your account. Interest is charged on any tax not paid by the due date of the original return, without regard to extensions.

5. When amending multiple paper filed returns, send them in separate envelopes. Sometimes when filed together, they are mistaken for a single return, and the additional returns filed in the same envelope are not processed.

6. If the changes involve a new schedule or form that wasn’t part of the original return, it must be completed and included with the amended return. And if there are changed forms, they must be included as well. In addition, it may be appropriate to include documentation related to the changes to avoid subsequent correspondence from the IRS or state agency.

7. A detailed explanation of the changes must also be included. This is required to explain to the government’s processing staff the reason for the amendment. An insufficient explanation can lead to additional correspondence and delays.

8. Depending on why an amended federal return is required, it may be necessary to amend your state return. However, if the federal amendment is filed to claim or correct a tax credit that the state does not have, no state amended return will likely need to be filed. In most other circumstances, we will need to amend the state return as well as the federal.

An amended return can be more complicated than the original, so please see your tax preparer for assistance in with an amended return.