Updated October 18, 2026. Quick answer: Lines 5 to 13 turn your net earnings into the tax. Line 6 is your total subject to the tax, line 7 is the 2025 social security base, lines 8 and 9 reduce that base by wages already taxed, line 10 applies 12.4% and line 11 applies 2.9%. Line 12 is the self-employment tax and line 13 is the one-half deduction.
Related reading on this site: IRS Publication 334.
Form lines read one part at a time: Form 8959 Part II.
What lines 5 to 6 ask for
Lines 5a and 5b are only for church employee income. Line 5a says “Enter your church employee income from Form W-2.” and line 5b says “Multiply line 5a by 92.35% (0.9235). If less than $100, enter-0-”. Most readers leave these blank. Line 6 then says “Add lines 4c and 5b”, where line 4c comes from the Schedule SE lines 1 to 4 page.
Line 7: the social security base
Line 7 prints the limit for the year. The form words it as “Maximum amount of combined wages and” self-employment “earnings subject to social security tax or the 6.2% portion of the 7.65% railroad retirement (tier 1) tax for 2025”. The instructions repeat the figure: “For 2025, the maximum amount of” self-employment “income subject to social security tax is $176,100.”
Lines 8 and 9: wages already taxed
If you also had a job, the wages you already paid social security tax on use up part of the base. Line 8a is “Total social security wages and tips (total of boxes 3 and 7 on Form(s) W-2)” and railroad retirement compensation, line 8b is “Unreported tips subject to social security tax from Form 4137, line 10” and line 8c is “Wages subject to social security tax from Form 8919, line 10”. Line 8d says “Add lines 8a, 8b, and 8c”.
The form has a shortcut on line 8a: “If $176,100 or more, skip lines 8b through 10, and go to line 11”. Otherwise line 9 says “Subtract line 8d from line 7. If zero or less, enter-0- here and on line 10 and go to line 11”.
Lines 10 and 11: the two rates
Line 10 is “Multiply the smaller of line 6 or line 9 by 12.4% (0.124)”. Line 11 is “Multiply line 6 by 2.9% (0.029)”. The smaller-of rule on line 10 is how the base on line 7 limits the social security part, while line 11 applies to line 6 in full.
Line 12: the self-employment tax
Line 12 adds the two rates together. The form says “Add lines 10 and 11. Enter here and on Schedule 2 (Form 1040), line 4”. The line feeds the figure explained on the Schedule 2 line 4 page, and self-employment tax explained gives the wider picture.
Here is a labelled illustration of the form’s own arithmetic, computed step by step, not an IRS example. Suppose line 6 were $40,000 and line 8d were zero, so line 9 would be $176,100 minus zero, and the smaller of line 6 and line 9 is line 6. Line 10 would be $40,000 multiplied by 0.124, which is $4,960. Line 11 would be $40,000 multiplied by 0.029, which is $1,160. Line 12 would be the sum of $4,960 and $1,160 and comes to $6,120. Line 13 would be computed as half of that sum, $3,060.
Line 13: the one-half deduction
Line 13 is “Multiply line 12 by 50% (0.50). Enter here and on Schedule 1 (Form 1040), line 15”. In the illustration above, half of $6,120 is $3,060. The deduction is explained with the related lines on the Schedule 1 lines 15 and 16 page. The instructions add that for this line, “If you are filing Form 1040-SS, skip this line.”
A note on the Additional Medicare Tax
The instructions also flag a separate tax on high earners: a 0.9% Additional Medicare Tax “may apply to you if the total amount on line 6 of all your Schedules SE exceeds one of the following threshold amounts”. The thresholds depend on filing status and are listed in the instructions for line 13. The calculation is done on Form 8959, so use the instructions for that form.
Where it goes next
The tax from line 12 goes to Schedule 2 line 4 and from there into Form 1040, and the deduction from line 13 goes to Schedule 1 line 15. The overview of the whole schedule is on the Schedule SE (Form 1040) page, and the Schedule C profit that usually starts the calculation is on the Schedule C (Form 1040) page.
Edition and line numbers
This page reads the 2025 Schedule SE (Form 1040) and its 2025 instructions, the current files irs.gov served on 2026-10-18 (byte-identical to the archived copies). They are the files for the tax year 2025 return, filed in 2026. The schedule says “Attach to Form 1040, 1040-SR, 1040-SS, or 1040-NR.” 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
- Applying 12.4% to the whole of line 6. Line 10 says “Multiply the smaller of line 6 or line 9 by 12.4% (0.124)”.
- Leaving out W-2 wages on line 8a. The line asks for “Total social security wages and tips (total of boxes 3 and 7 on Form(s) W-2)”.
- Treating the line 13 deduction as part of the tax. The form says “Multiply line 12 by 50% (0.50). Enter here and on Schedule 1 (Form 1040), line 15”.
Related: Schedule 2 line 4, self-employment tax explained, Schedule 1 lines 15 and 16, Schedule C (Form 1040), and Form 1040.
Sources
- Instructions for Schedule SE (Form 1040), Self-Employment Tax (2025): https://www.irs.gov/pub/irs-pdf/i1040sse.pdf
- Schedule SE (Form 1040), Self-Employment Tax (2025): https://www.irs.gov/pub/irs-pdf/f1040sse.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.