How to File a Maryland Amended Tax Return: Form 502X and Deadlines

To amend a Maryland state income tax return, full-year residents file Form 502X and nonresidents or part-year residents file Form 505X with the Comptroller of Maryland. If the amendment is triggered by an IRS change that increases your Maryland tax, you have 90 days from the federal determination to file. If a federal change decreases your Maryland tax, you have one year to claim the refund. For errors you find on your own, the standard refund deadline is three years from when the original return was due or filed, whichever is later.

Which Form to File

Two forms cover almost every situation:

Form 502X, for full-year Maryland residents amending a previously filed Form 502.¹
Form 505X, for nonresidents and part-year residents amending a previously filed Form 505.²

If your amendment changes your status from nonresident to resident, use Form 502X rather than 505X.² Always pull the version of the form that matches the tax year you are correcting, not the current year’s version. Forms are available on the Comptroller’s website.

The 90-Day Rule After a Federal Change

Maryland’s tax calculation begins with your federal adjusted gross income, so any change to your federal return flows through to your state return. When you file a federal Form 1040-X or the IRS makes a final determination that adjusts your federal figures, you are required to file a corresponding Maryland amended return.³

The deadline depends on which way the change runs:

If the federal change increases your Maryland tax, you must file the amended Maryland return within 90 days of the IRS’s final determination.²
If the federal change decreases your Maryland tax, you have one year from the IRS’s final determination to file for a refund.²

The 90-day window is short, and missing it is costly. If you fail to notify the Comptroller within 90 days of a federal determination that increases your state tax, there is no statute of limitations on the Comptroller’s ability to assess the additional tax.⁴ Notify within 90 days and the Comptroller has one year to assess any deficiency, after which the matter closes.

Deadlines When You Discover the Error Yourself

If no federal change is involved, the standard deadline for claiming a Maryland refund is three years from the date the original return was due (including extensions) or three years from the date it was filed, whichever is later.² A claim filed after three years but within two years of when the tax was actually paid is limited to the amount paid during the two years immediately before filing.

Common reasons to amend on your own include forgetting to report income from a W-2 or 1099, miscalculating a deduction, using the wrong filing status, or missing a Maryland credit or subtraction you were entitled to.

Documents to Attach

Gather your paperwork before touching the form. If the amendment stems from a federal change, attach a complete copy of your federal Form 1040-X and any revised federal schedules.³ Maryland requires the income and deductions on your state return to match your federal return, so the federal paperwork is the backbone of the amendment.

For income corrections, include corrected W-2c forms, amended 1099s, or revised K-1 schedules. For a new or adjusted credit or deduction, attach the full supporting schedule or worksheet. Missing documentation slows processing or triggers follow-up correspondence from the Comptroller.

How the Three-Column Calculation Works

Both Form 502X and Form 505X use a three-column layout that isolates exactly what changed:

Column A holds the figures from your return as originally filed.
Column B holds the net increase or decrease on each line.
Column C holds the corrected figures.

Work line by line. If your corrected federal AGI in Column C is $5,000 higher than the original in Column A, enter +$5,000 in Column B on that line. Column A plus or minus Column B should always equal Column C. The most common error is a Column C figure that does not reconcile with the other two columns on the same line.

Recalculating Your State and Local Tax

Once the corrected income figures are in place, recalculate the state tax using the rate schedule for the tax year you are amending. Maryland’s income tax is progressive, with marginal rates from 2% on the first $1,000 of taxable income up to 6.5% on income above $1,000,000 for single filers or above $1,200,000 for joint filers.⁵

Do not skip the local income tax. Every county and Baltimore City imposes a local income tax on the same taxable income, currently ranging from 2.25% to 3.30%.⁶ When your taxable income changes, the local tax changes with it. Apply the rate for the county where you lived on the last day of the tax year.

Compare the recalculated total to what you originally paid. If you overpaid, you are owed a refund. If you underpaid, you owe the difference plus interest.

Interest and Penalties If You Owe

Interest on an underpayment accrues from the original due date of the return, not from the date you discovered the error. Through December 31, 2026, Maryland’s interest rate is 10.8133% per year.² That adds up quickly.

The Comptroller can also assess a penalty of up to 10% of the unpaid tax for failure to pay when due or failure to file a required return.³ A false or fraudulent return carries steeper civil and criminal penalties, including potential imprisonment. If you owe, file and pay as soon as you can, and send payment with the amended return to stop interest from continuing to build during processing.

Where to Send the Return

Sign the form, attach your supporting documents, and mail the package to:

Comptroller of Maryland
Revenue Administration Division
110 Carroll Street
Annapolis, MD 21411-0001¹

If you owe, include a check or money order payable to “Comptroller of Maryland,” or pay through the Comptroller’s online payment portal. Maryland’s iFile system has accepted amended returns electronically for some prior tax years; check the iFile portal to see whether the year you are amending is listed.⁷ Electronic filing is required if you are claiming or adjusting a business income tax credit from Form 500CR.⁸ For most amendments, paper filing remains standard.

Amended returns take significantly longer than original returns to process. Expect several weeks to a few months for a refund or a notice, and keep a copy of everything you send.

1
Comptroller of Maryland. Individual Tax Forms and Instructions
2
Comptroller of Maryland. Maryland Form 505X Nonresident Amended Tax Return
3
Comptroller of Maryland. Maryland Nonresident Tax Forms and Instructions
4
Comptroller of Maryland. General Audit / Statute of Limitations
5
Maryland General Assembly. Maryland Code Tax-General 10-105
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Comptroller of Maryland. Withholding Tax Facts January 2026
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Comptroller of Maryland. iFile Choose Form Entrance
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Comptroller of Maryland. Form 502X Amended Tax Return