Updated October 17, 2026. Quick answer: Line 17z is the catch-all for taxes not reported elsewhere: you list the type of tax and the amount. Line 18 is the total of lines 17a through 17z, so it adds every entry in the line 17 list. The amount on line 18 is then carried into the total on line 21.
Line 17z: any other taxes
The form’s caption reads “Any other taxes. List type and amount”. The instructions say “Use line 17z to report any taxes not reported elsewhere on your return or other schedules. List the type and amount of tax.” “Other taxes to be listed include the following.” The first item is “The prevailing wage and apprenticeship penalties (PWA) from Form 4255”, and for each of the three penalty cases listed under it they say “If you entered an amount in more than one column, enter the total on line 17z.”
Form 8978 adjustment
The second item on the list is a Form 8978 adjustment. The instructions say “Complete the Negative Form 8978 Adjustment Worksheet” “if you are filing Form 8978 and completed the worksheet in the Schedule 3, line 6l, instructions and the amount on line 3 of that worksheet is negative.” The worksheet itself is in the Form 1040 instructions, and this page does not copy its entries. If that situation applies to you, work through the worksheet by name and follow its directions for what to list on line 17z.
Form 8621 and line 17z
The instructions add a caution for filers of Form 8621: do not enter the amount from line 9c on line 17z. Instead, “see the Instructions for Form 8621 for how to report this amount.” The page on Form 8621 covers that form, and lines 17p and 17q of this schedule take other amounts from it.
Line 18: total additional taxes
The form’s caption reads “Total additional taxes. Add lines 17a through 17z”. The instructions for the schedule contain no separate paragraph for line 18, so the caption is the rule: add every entry from line 17a through line 17z and enter the total.
Where the number comes from
For line 17z, the amounts come from the forms and worksheets the instructions name, and the type of tax is written beside the amount. For line 18, the number is the sum of the entries you made on lines 17a through 17z. No outside statement supplies it.
Where it goes next
Line 18 feeds line 21. The caption for line 21 reads “Add lines 4, 7 through 16, 18, and 19.” “These are your total other taxes.” Line 21 is covered in Schedule 2 lines 19 to 21. The earlier lines of the list are on the pages for lines 17l to 17q. The layout of the whole schedule is on the Schedule 2 (Form 1040) page, and the return is explained on the Form 1040 line by line 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 an amount on line 17z without saying what it is. The instructions say “List the type and amount of tax.”
- Entering only one column of a penalty amount. The instructions say “If you entered an amount in more than one column, enter the total on line 17z.”
- Leaving a line 17 entry out of line 18. The caption reads “Total additional taxes. Add lines 17a through 17z”.
Related: Form 8621, Form 1040 line by line, and Form 1040.
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.