Updated October 18, 2026. Quick answer: Part III of Form 8959 is for railroad retirement (RRTA) compensation. It starts from W-2 box 14, compares the amount with the figure printed for your filing status, and multiplies any excess by 0.9%. The result on line 17 carries to Part IV.
Read box by box from the IRS form text: Form RRB-1099-R boxes 7 to 12.
What this part is for
Part III applies to railroad employees: “didn’t have RRTA compensation, skip Part III and go to Part IV” is the instruction for everyone else. It is one piece of Form 8959, after Form 8959 Part II.
RRTA pay is kept apart from wages and self-employment income: “RRTA compensation should be separately compared to the threshold.” “There is no equivalent rule for RRTA compensation.”
The lines, one by one
| Line | What the form says |
|---|---|
| 14 | “Railroad retirement (RRTA) compensation and tips from Form(s) W-2, box 14” “(see instructions)” |
| 15 | “Enter the following amount for your filing status:” The form prints the same filing status amounts as on lines 5 and 9. |
| 16 | “Subtract line 15 from line 14. If zero or less, enter” “-0-“. |
| 17 | “Additional Medicare Tax on railroad retirement (RRTA) compensation. Multiply line 16 by 0.9% (0.009).” “Enter here and go to Part IV”. |
Where the number comes from
Line 14 comes from the W-2: “The amount of RRTA compensation for a railroad employee is reported on Form W-2, box 14.” “If you have more than one Form W-2, enter the total of the RRTA compensation amounts from box 14 of all Forms W-2.” “If you are filing a joint return, also include your spouse’s RRTA” compensation. Other W-2 boxes are explained in W-2 box 1, box 3 and box 5.
The instructions give a rule for one more group: “An employee representative subject to RRTA taxes should include the total compensation subject to Tier 1 Medicare tax as reported on line 2 of Form CT-2”.
Line 17 is described this way: “Multiply line 16 by 0.9% (0.009). This is your Additional Medicare Tax on RRTA compensation.”
Where it goes next
The instructions say “Enter the result on this line and go to Part IV”. Part IV adds the three parts together, see Form 8959 Parts IV and V, and the total reaches Schedule 2 lines 10 and 11. For a related RRTA item on the return, see Schedule 3 line 11. Wider context is in Additional Medicare Tax.
A worked example
Illustration, not an IRS example. The inputs are invented, and the line 15 amount is a stand-in chosen only for easy arithmetic; it is not the amount printed for any filing status.
| Line | Amount in the illustration |
|---|---|
| Line 14 | $70,000 (invented, for the computation) |
| Line 15 (stand-in) | $60,000 (invented, for the computation) |
| Line 16 | $10,000 (computed) |
| Line 17 | $90 (computed) |
Line 16 is 70,000 minus 60,000, which is 10,000. Line 17 is 10,000 x 0.009, which is 90.
Edition and line numbers
This page reads Form 8959 for 2025 and its 2025 instructions, the current files irs.gov served on 2026-10-18. Check the edition printed on your own form and use that edition’s line numbers.
Common mistakes
- Adding RRTA pay into the wage or self-employment lines. The instructions say “RRTA compensation should be separately compared to the threshold.”
- Using the wrong W-2 box. The instructions say “The amount of RRTA compensation for a railroad employee is reported on Form W-2, box 14.”
- Dropping a second W-2. The instructions say “If you have more than one Form W-2, enter the total of the RRTA compensation amounts from box 14 of all Forms W-2.”
Related: Form 8959, Additional Medicare Tax, W-2 box 1, box 3 and box 5, Schedule 2 lines 10 and 11, and Schedule 3 line 11.
Sources
- Form 8959 (2025), Additional Medicare Tax: https://www.irs.gov/pub/irs-pdf/f8959.pdf
- 2025 Instructions for Form 8959: https://www.irs.gov/pub/irs-pdf/i8959.pdf
- IRS: About Form 8959: https://www.irs.gov/forms-pubs/about-form-8959
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.