Amended returns

[SCswede]

After filing my 2024 Federal and state returns and receiving both refund checks I received a corrected 1099-B from my brokerage firm's investment fund which adjusted the cost basis of several stock sales transactions. It resulted in and increase of LT Capital gain of $330 and Taxable Income and Federal Tax due of $49 and State tax of $12. Aside from the 1040-X for Federal, the State's AMD form and an explanation of the reason for the amended returns, what other forms do I need to attach to the Amended returns?

Also, am I subject to any interest or penalty even though this issued was not my fault?

Thanks for any input and guidance.

[fanfare]

Penalties:
1040-x Line 16: Subtract any penalty from the amount you owe reported on original 1040.
Don't try to include, but ignore, any new or changed penalty.
IRS will calculate your new penalty on their own and will bill you.

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If you are e-Filing 1040-X, TurboTax decides what forms to include.

@SCswede 

[rjs]

For the federal amended return you have to attach any forms or schedules that changed. That would include at least Schedule D, plus Form 8949 if that form is included in your tax return. You also have to attach any other forms or schedules that changed because of the change in the amount of income. The explanation of changes is included on Form 1040-X. It is not a separate attachment.

For the state amended return, see the instructions for your state's form. If you say what state it is, someone might be able to give you more specific information. Every state has different forms and rules.

You would be subject to interest and penalties for late payment. It's your responsibility to report the correct basis from your own records, even if the 1099-B is wrong. But for such small amounts of additional tax, and only a short time since the payment deadline, the interest and penalties are not going to amount to much. The IRS and the state might not even bother to bill you for it.