NJ-1040X Instructions for Amending Your NJ Tax Return

An amended tax return allows you to correct mistakes or update information on a previously filed New Jersey resident income tax return, Form NJ-1040. You must use Form NJ-1040X for this purpose, as filing a new NJ-1040 will cause processing delays. File the NJ-1040X only after your original return has been fully processed by the New Jersey Division of Taxation. An amended return may result in a refund of overpaid taxes or a bill for additional taxes owed.

Gathering Necessary Information and Documents

Before amending your New Jersey tax return, organizing all required documentation ensures accuracy. The current year’s Form NJ-1040X and its instructions can be downloaded from the New Jersey Division of Taxation’s website.

You will need the following:

• A complete copy of the original NJ-1040 return you are amending, which serves as the baseline for your figures.
• A copy of the federal Form 1040-X and the corrected IRS Form 1040, if the changes result from federal adjustments. New Jersey requires you to report federal changes within 90 days of the final determination from the IRS.
• All supporting documents that substantiate the changes, such as corrected wage statements (Form W-2c), updated income documents (Forms 1099), or revised schedules.
• The correct Social Security numbers for yourself, your spouse, and any dependents as they appeared on your original return.

Step-by-Step Guide to Completing Form NJ-1040X

Once you have your documents, you can begin completing Form NJ-1040X. The top of the form requires basic identifying information. You must enter the calendar year of the return you are amending, your name, Social Security Number, and current address. If you filed a joint return, include your spouse’s name and Social Security Number in the same order as they appeared on the original NJ-1040.

The next part of the form addresses your filing status and exemptions. If you are changing your filing status, you must select the new status. Note that you generally cannot change from married filing jointly to a separate filing status after the original tax deadline has passed. You will also report the number of exemptions as originally claimed and the corrected number.

The core of Form NJ-1040X is its three-column format. Column A, “As Originally Reported,” is where you will transfer the figures directly from your initial NJ-1040. This column should be a precise copy of what the state already has on record.

Column B, “Net Change,” is where you will input the specific adjustments. For each line item that needs correction, you will enter the amount of the increase or decrease. A negative number, indicated with a minus sign or parentheses, signifies a decrease.

Column C, “Corrected Amount,” is the result of your calculations. For each line, you will add the figure in Column B to the figure in Column A to arrive at the new, correct total. After completing the income, deduction, and credit sections, you must provide a detailed explanation for each change, referencing the specific line numbers affected. This narrative is a mandatory part of the return.

Submitting Your Completed Amended Return

After you have filled out Form NJ-1040X, you must assemble the complete package for submission. You cannot file an amended New Jersey return electronically; it must be mailed. Your submission must include the signed NJ-1040X and all supporting schedules and forms that justify the changes, such as corrected W-2s or 1099s.

All completed Form NJ-1040X submissions should be mailed to:
State of New Jersey
Division of Taxation
Revenue Processing Center
PO Box 664
Trenton, NJ 08646-0664

If you owe additional tax, you can pay online through the Division of Taxation’s website. Alternatively, you can include a check or money order with your mailed return, made out to “State of New Jersey – TGI.” To ensure the payment is applied correctly, write your Social Security number and the tax year you are amending on the memo line of the check.

What to Expect After Filing

After mailing your Form NJ-1040X, you should anticipate a significant processing period. It can take up to three weeks for a mailed return to be entered into the state’s system, after which you can check its status online. The Division of Taxation advises that overall processing can take up to 16 weeks, while returns that require manual review may take 12 weeks or longer.

You can monitor the progress of your amended return through the state’s “Check Your Refund Status” tool on the Division of Taxation’s website. To use this service, you will need to provide your Social Security number and the exact amount of the expected refund as calculated on your NJ-1040X.

Once processing is complete, the outcome will be communicated by mail. If your amendment results in a refund, you will receive a paper check. If you owe additional tax, you will receive a Notice of Adjustment and a bill for the amount due, which may include interest. Interest is charged on any underpayment from the original due date of the tax return until the date of payment, at a rate set at 3% above the prime rate. For 2025, the interest rate is 10.75%.