NIIT and Additional Medicare Tax in Estimated Tax
Checked October 17, 2026 · Educational summary
General information, not tax, legal or financial advice. We are not the IRS. Check IRS.gov or a qualified tax professional. Sources read on October 17, 2026. Dates for 2027 and later are expected. Examples use made-up numbers. This page contains no affiliate links.
Publication 505 (2026) says the Net Investment Income Tax (NIIT) and the 0.9% Additional Medicare Tax may need to be included when you figure estimated tax. Each applies above a threshold that depends on filing status.
Thresholds listed in Pub. 505 (2026)
| Filing status | Additional Medicare Tax (0.9%) on wages + self-employment income over | NIIT: 3.8% of the lesser of net investment income or the amount by which MAGI exceeds |
|---|---|---|
| Single | $200,000 | $200,000 |
| Head of household | $200,000 | $200,000 |
| Married filing jointly | $250,000 | $250,000 |
| Qualifying surviving spouse | $200,000 | $250,000 |
| Married filing separately | $125,000 | $125,000 |
| Note the qualifying surviving spouse figures differ between the two taxes in the pub's tables. |
How they enter the estimate
- The pub's worksheet instructions say to add these taxes among your expected taxes (Step 2 of "Expected Taxes and Credits"), along with AMT and others.
- Additional Medicare Tax: Medicare wages and self-employment income are combined for the threshold; a self-employment loss is not considered. Your employer is responsible for withholding it on wages over $200,000, and the pub says to consider that withholding when deciding whether to make an estimated payment.
- NIIT: the pub says it "may need to be included" and that you may ask your employer to withhold more income tax on Form W-4 to cover it.
- Estimated tax covers income tax and other taxes such as self-employment tax and AMT (IRS estimated-tax page, reviewed 25 September 2026).
Illustration (made-up)
Single filer, MAGI $230,000, net investment income $50,000: the excess over $200,000 is $30,000, which is lower than $50,000, so the NIIT base is $30,000 and the tax is $30,000 × 3.8% = $1,140. This is only the pub's formula applied to made-up numbers, not a calculation of your return (see Form 8960 and its instructions, which we did not read).
Practical points
- Start from last year's return, as the IRS suggests, and adjust for changes. See Form 1040-ES worksheet step by step.
- If income jumps mid-year, see amended worksheet.
- Self-employment tax basics: SE tax guide.
- Next payment for 2026: January 15, 2027 (dates).
FAQ
Does investment income always trigger NIIT?
No: it depends on the thresholds and your net investment income; the pub's definition of net investment income is in Form 8960 instructions (not read).
Are the thresholds indexed?
The pub shows these amounts for 2026. We have not checked whether they change for 2027 (Pub. 505 and forms for 2027 are not published).
What we could not verify
- Form 8960 and its instructions (definition of net investment income) were not read.
- Whether 2027 thresholds change.
- Your own MAGI and investment income.
Sources
- IRS, Publication 505 (2026), Tax Withholding and Estimated Tax, Reminders and chapter 2 — https://www.irs.gov/publications/p505 (PDF read 17 October 2026)
- IRS, Estimated taxes — https://www.irs.gov/businesses/small-businesses-self-employed/estimated-taxes (read 17 October 2026; reviewed or updated 25 September 2026)