Let’s say you submitted your tax return by the deadline, but in June you discovered you neglected to include revenue from a freelancing job last summer. No need to worry; all you have to do is file an updated return on Form 1040-X.

Here’s what you need to know about filing amended returns –

1. When to use Form 1040-X

In general, you must submit Form 1040X within three years of filing your initial tax return or two years after paying the tax, whichever is later. Make sure to specify the year of the return you are amending at the top of Form 1040X.

You will be able to correct any mistakes, including:

• Filing status
• Exemptions
• Income
• Deductions or credits

2. Not all mistakes require an amended return

You do not need to submit a 1040-X if your original return has mathematical inconsistencies or is missing paperwork, such as a W-2. The IRS will normally fix and alert you of these issues, as well as any missing paperwork.

3. Amended return timing

If the adjustment results in you owing money, file as quickly as possible to avoid any penalties or interest that may apply. Although the IRS appreciates it when taxpayers file an updated return to fix a mistake, they can still impose a penalty or levy interest for failing to pay the correct amount when taxes were due. If the adjustment resulted in a tax refund and you have yet to receive it, do not file the updated return until you have received it to prevent difficulties.

4. Preparing the amended return

To complete a Form 1040-X, you’ll need:

• A copy of the original tax return that’s being amended
• W-2s
• Schedules
• Worksheets
• Corrected information and calculations
• Any forms needed to support corrections

Do not include the original return with the 1040-X.

5. Stating the reason for the amended return

Form 1040-X, Part III, requires you to explain in your own words why you are modifying the return. This explanation should describe the exact changes you’re making and might be brief. Reasons may include:

You forgot to claim the Child Tax Credit.

You have received an additional, or updated W-2 form.

You omitted a charitable donation.

6. What Happens When You Owe Money

If you owe money as a consequence of the amendment, include a check or money order to your 1040-X filing. You can pay your outstanding debt online using Direct Pay or the Electronic Federal Tax Payment System (EFTPS). If you are unable to pay right now, file an updated return and apply for an IRS Installment Plan.

7. Mailing instructions for paper-filed amended returns

Each amended tax return requires its own Form 1040-X, which should be submitted in a separate envelope. Mail the completed form to the address specified in the Form 1040-X instructions.

8. Amending your state tax return

After submitting Form 1040-X, check to see whether your state tax form also needs to be amended. If so, get the appropriate form from your state’s tax department and utilize the information on the federal 1040-X to help you fill it out. Be sure to include a copy of your 1040-X with your state amended return.