What this line means
Multiply line 4c (total SE earnings) by 2.9% (0.029). This is the Medicare tax portion of your self-employment tax. Unlike Social Security tax, Medicare has no wage base limit — every dollar of SE earnings is subject to the 2.9% rate regardless of how much you earned from employment. This line applies even if you skipped line 9 because your W-2 wages consumed the entire Social Security ceiling.
Does this apply to you?
Easy to overlook
The 0.9% Additional Medicare Tax is separate and not included here Line 10 calculates only the standard 2.9% Medicare tax. If your SE income exceeds $200,000 ($250,000 married filing jointly), an additional 0.9% Medicare tax applies — but that is calculated on Form 8959, not on Schedule SE. Filers who expect line 10 to capture their full Medicare obligation underreport if they have high earnings. Form 8959 must be filed separately. 1 IRS Form 8959 instructions — Additional Medicare Tax
Medicare tax applies to all SE earnings, even above the Social Security cap A filer with $300,000 in SE earnings and no W-2 wages pays Social Security tax on only $176,100 of those earnings — but pays Medicare tax on the full $300,000. Line 10 is $8,700 (2.9% of $300,000), while line 9 is $21,836 (12.4% of $176,100). There is no ceiling on Medicare, and the 2.9% rate applies to the total amount. 2 IRS Schedule SE instructions — Line 10
Watch out for this
Adding the 0.9% Additional Medicare Tax to this line. Line 10 is strictly the 2.9% base Medicare tax. The additional 0.9% surtax for high earners belongs on Form 8959 and flows to Schedule 2, line 23. Including it on line 10 double-counts the additional tax since Form 8959 is filed regardless of what appears on Schedule SE.
Footnotes
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IRS Form 8959 Instructions, Additional Medicare Tax. https://www.irs.gov/instructions/i8959 ↩
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IRS Schedule SE (Form 1040) Instructions, Line 10. https://www.irs.gov/instructions/i1040sse ↩