Updated October 17, 2026. Quick answer: Line 4 is self-employment tax. The amount comes from Schedule SE, line 12. Three boxes beside the line are for the cases the instructions describe: Form 4361, Form 4029, and a third box for other situations.
More IRS forms and schedules, read line by line: Form 8919 uncollected social security tax.
S corporation return (Form 1120-S) for 2025, read line by line: Form 1120-S Schedule K lines 1 to 4.
Partnership return (Form 1065) for 2025, read line by line: Form 1065 lines 9 and 10, Form 1065 Schedule K lines 1 to 4 and Form 1065 Schedule K lines 12 to 14.
Schedule C and Schedule SE (Form 1040) for 2025, read line by line: Schedule C lines 2 to 5, Schedule C lines 16a and 16b and Schedule C lines 17 to 19.
What line 4 asks for
The form’s caption reads “Attach Schedule SE.” The instructions give the number: “On line 4, enter the amount of the tax due on net earning from self-employment from Schedule SE, line 12.” For the tax itself and how it differs from income tax, see self-employment tax explained. The business income behind it is usually reported on Schedule C.
Where the number comes from
The figure is the Schedule SE result, so line 4 is a copy rather than a calculation. The instructions close the topic with “For more information, see the Instructions for Schedule SE.”
The exemption boxes
Box 1: “If you filed Form 4361, received IRS approval, and had no other income subject to” self-employment tax, “check box 1 on line 4.” Box 2: “If you filed Form 4029 and received IRS approval, check box 2 on line 4.” The instructions add “See Pub. 517 for details.”
Box 3 covers other cases. For a U.S. citizen or resident alien living outside the United States whose self-employment income is exempt from self-employment tax, the instructions say to get a statement from the appropriate agency of the foreign country verifying that the income is subject to social security in that country, attach a copy of the statement, check box 3, and enter “EAS” on the entry space next to box 3. For a notary public they say “If you received fees for services performed as a notary public and you had no other income subject to self-employment tax, check box 3”, and add that if there were other earnings, “If you did have other earnings of $400 or more subject to self-employment tax” a different entry applies. Read the full text of each case in the Form 1040 instructions.
Where it goes next
Line 4 is added into the Part II total. The caption for line 21 reads “Add lines 4, 7 through 16, 18, and 19. These are your total other taxes.” The instructions send the result to the return: “Enter the amount on Schedule 2, line 21, on Form 1040 or 1040-SR, line 23”. See the Form 1040 lines 22, 23 and 24 page, the Schedule 2 (Form 1040) page, and the Form 1040 page.
Edition and line numbers
This page reads the 2025 Schedule 2 (Form 1040) and the 2025 Form 1040 instructions, the current files irs.gov served on 2026-10-17. They are the files for the tax year 2025 return, filed in 2026. The schedule says “Attach to Form 1040, 1040-SR, or 1040-NR.” Its line instructions are part of the Form 1040 instructions, under the heading “Instructions for Schedule 2”. Check the tax year printed on the schedule you are filling in and use the line numbers on that year’s schedule, because a different year’s schedule can number or word its lines differently.
Common mistakes
- Entering net profit instead of the tax. The instructions say to enter “the amount of the tax due on net earning from self-employment from Schedule SE, line 12.”
- Checking box 1 without the approval. The instructions say “If you filed Form 4361, received IRS approval” before box 1 applies.
- Checking box 2 without the approval. The instructions say “If you filed Form 4029 and received IRS approval, check box 2 on line 4.”
Related: self-employment tax explained, Schedule C, and Form 1040 lines 22, 23 and 24.
Sources
- Instructions for Form 1040 and Form 1040-SR (2025): https://www.irs.gov/pub/irs-pdf/i1040gi.pdf
- Schedule 2 (Form 1040), Additional Taxes (2025): https://www.irs.gov/pub/irs-pdf/f1040s2.pdf
Read from the IRS documents linked above on October 17, 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.