Updated October 18, 2026. Quick answer: Part I is the Dependents section of Form 1040-X. You complete it only to change dependent information. Lines 24, 26, 28 and 29 are reserved and stay empty, lines 25 and 27 count dependents in the same A, B and C columns, and line 30 lists every dependent claimed on the amended return.
When you complete Part I
The form says “Complete this part to change any information relating to your dependents.” “This would include a change in the number of dependents.” It also says “Enter the information for the return year entered at the top of page 1.” The part has its own columns: column A is the “Original number of dependents reported or as previously adjusted”, column B is the net change, and column C is the correct number.
Lines 24, 26, 28 and 29: reserved
The instructions say “These lines are reserved for future use. Do not enter an amount on these lines.” The form prints “Reserved for future use” beside each of them.
Lines 25 and 27: the dependent counts
Line 25 is captioned “Your dependent children who lived with you more than half of the year” and line 27 is captioned “Other dependents”. The instructions have no separate paragraph for line 25 or line 27, so use the form’s captions and the Dependents instructions for the return year you are amending, which the line 30 instructions point to. Fill in column A from the original return, column B with the increase or decrease, and column C with the correct number.
Computed illustration, not an IRS example: if column A of line 27 showed 1 dependent and you added 2, column C would be 1 plus 2, which is 3.
Line 30: list all dependents
The form’s caption is “List ALL dependents (children and others) claimed on this amended return.” The instructions say “List all dependents claimed on this amended return.” That includes:
- “Dependents claimed on your original return who are still being claimed on this return, and”
- “Dependents not claimed on your original return who are being added to this return.”
The instructions then send you elsewhere: “See Dependents, in the instructions for the tax return for the year you are amending, for more information.”
Where the number comes from
The counts and names come from the return you are amending and from the dependents you now claim. The credits tied to dependents are figured on the tax side of the form; see the lines 6 to 11 page, and the original-return credit pages such as Form 1040 lines 19 to 21.
Where it goes next
Part I ends the numbered lines, and the next section is Part II, where the form says “You must complete Part II.” It is covered on the Parts II and III page. The payments and refund sections are on the lines 12 to 17 and lines 18 to 23 pages.
Edition and line numbers
This page reads the December 2025 revision of Form 1040-X and its December 2025 instructions, the current files irs.gov served on 2026-10-18. The form is marked “(Rev. December 2025)” and it amends the return year the filer enters at the top, so the revision date is not the same thing as the year being amended. The form’s own instruction at the top says “Attach a completed Form 1040, 1040-SR, or 1040-NR, with your changes, for the return year entered below”. Check the revision date printed on the form you are filling in and the return year you are amending, and use the line numbers on that revision, because a different revision can number or word its lines differently. The whole form is walked through on the Form 1040-X walkthrough page.
Common mistakes
- Entering an amount on a reserved line. The instructions say “Do not enter an amount on these lines.”
- Listing only the new dependents on line 30. The instructions say “List all dependents claimed on this amended return.”
- Using the amended return year’s rules from memory. The instructions say “See Dependents, in the instructions for the tax return for the year you are amending, for more information.”
Related: Form 1040 lines 19 to 21, child tax credit, Form 1040 line 28, and Form 1040 line by line.
Sources
- Instructions for Form 1040-X, Amended U.S. Individual Income Tax Return (Rev. December 2025): https://www.irs.gov/pub/irs-pdf/i1040x.pdf
- Form 1040-X, Amended U.S. Individual Income Tax Return (Rev. December 2025): https://www.irs.gov/pub/irs-pdf/f1040x.pdf
Read from the IRS documents linked above on October 18, 2026. General information, not tax advice. Your own facts decide the outcome, and a preparer, the account provider or the IRS is the right place to confirm anything consequential.