Additional Medicare Tax Calculator
Enter your filing status, W-2 wages, business pay, and rail pay. See your Form 8959 tax, what your boss held back, and your net bill or credit.
Last reviewed
Your Form 8959 Additional Medicare Tax and withholding reconciliation
Additional Medicare Tax (Form 8959, Line 18)
$675.00
Additional Medicare Tax still owed
$675.00
Overwithheld credit (Form 1040, Line 25c)
$0.00
Tax on Medicare wages (Part I, Line 7)
$675.00
Tax on self-employment income (Part II, Line 13)
$0.00
Tax on RRTA compensation (Part III, Line 17)
$0.00
Additional Medicare Tax withheld (Part V, Line 24)
$0.00
Filing-status threshold (Part I, Line 5)
$250,000.00
Medicare wages above threshold (Part I, Line 6)
$75,000.00
Self-employment threshold after wages (Part II, Line 11)
$0.00
Self-employment income above reduced threshold (Part II, Line 12)
$0.00
Regular 1.45% Medicare tax on wages (Part V, Line 21)
$4,712.50
Effective Additional Medicare rate on combined pay
0.21%
Summary
Combined Medicare wages are $325,000.00 against the $250,000.00 joint threshold. Form 8959 adds $675.00 to Schedule 2, Line 11 and credits $0.00 on Form 1040, Line 25c, leaving $675.00 still to cover.
On $325,000.00 of joint W-2 pay, your floor is $250,000.00. That leaves $75,000.00 of wages subject to the surtax.
Line 18 adds $675.00 to Schedule 2 line 11. Line 24 credits $0.00 on Form 1040 line 25c, leaving $675.00 still due.
This tool covers Form 8959 Parts I to V (wages, business pay, rail pay, and Box 6 credits). Regular Medicare, Schedule SE, and income taxes are separate.
Your filing status, Medicare wages, self-employment pay, and withholding
- Combined wages = $325,000.00; Wage excess = $75,000.00
- Wage tax (Line 7) = $75,000.00 × 0.009 = $675.00
- SE excess (Line 12) = $0.00; SE tax = $0.00
- RRTA tax (Line 17) = $0.00; Withheld (Line 24) = $0.00
- Total Additional Medicare Tax (Line 18) = $675.00 + $0.00 + $0.00 = $675.00
Form 8959 total tax vs. mandatory employer withholding by wage level
Year-end balance due and overwithheld credit across wage levels
Form 8959 tax and withholding reconciliation across Medicare wage levels
Across the 8 preset Medicare wage levels ($100,000.00 to $400,000.00), Form 8959 tax moves from $225.00 to $2,925.00 and employer withholding moves from $0.00 to $1,800.00.
| Your wages | Wages over threshold | Total tax (Line 18) | Withheld (Line 24) | Balance due | Credit |
|---|---|---|---|---|---|
| $100,000 | $25,000.00 | $225.00 | $0.00 | $225.00 | $0.00 |
| $150,000 (closest to your input) | $75,000.00 | $675.00 | $0.00 | $675.00 | $0.00 |
| $175,000 | $100,000.00 | $900.00 | $0.00 | $900.00 | $0.00 |
| $200,000 | $125,000.00 | $1,125.00 | $0.00 | $1,125.00 | $0.00 |
| $230,000 | $155,000.00 | $1,395.00 | $270.00 | $1,125.00 | $0.00 |
| $250,000 | $175,000.00 | $1,575.00 | $450.00 | $1,125.00 | $0.00 |
| $300,000 | $225,000.00 | $2,025.00 | $900.00 | $1,125.00 | $0.00 |
| $400,000 | $325,000.00 | $2,925.00 | $1,800.00 | $1,125.00 | $0.00 |
Year-end Additional Medicare Tax still owed after employer withholding, by your Medicare wages (rows) and spouse's Medicare wages (columns).
| Your Medicare wages and tips (Form W-2, Box 5) by spouse's medicare wages and tips (Form W-2, box 5) | $0 | $100,000 | $175,000 | $250,000 |
|---|---|---|---|---|
| $100,000 | $0.00 | $0.00 | $225.00 | $450.00 |
| $150,000 (closest to your input) | $0.00 | $0.00 | $675.00 | $900.00 |
| $175,000 | $0.00 | $225.00 | $900.00 | $1,125.00 |
| $200,000 | $0.00 | $450.00 | $1,125.00 | $1,350.00 |
| $230,000 | $0.00 | $450.00 | $1,125.00 | $1,350.00 |
| $250,000 | $0.00 | $450.00 | $1,125.00 | $1,350.00 |
| $300,000 | $0.00 | $450.00 | $1,125.00 | $1,350.00 |
| $400,000 | $0.00 | $450.00 | $1,125.00 | $1,350.00 |
How Schedule SE self-employment income interacts with the Form 8959 wage threshold
As Schedule SE Line 6 self-employment income rises from $0.00 to $250,000.00 across the 8 rows, Part II tax grows from $0.00 to $2,250.00 and total Form 8959 tax moves from $675.00 to $2,925.00.
| SE income (Line 8) | Reduced SE threshold | Taxable SE excess | Part II SE tax | Total tax (Line 18) | Balance due |
|---|---|---|---|---|---|
| $0 (closest to your input) | $0.00 | $0.00 | $0.00 | $675.00 | $675.00 |
| $25,000 | $0.00 | $25,000.00 | $225.00 | $900.00 | $900.00 |
| $50,000 | $0.00 | $50,000.00 | $450.00 | $1,125.00 | $1,125.00 |
| $75,000 | $0.00 | $75,000.00 | $675.00 | $1,350.00 | $1,350.00 |
| $100,000 | $0.00 | $100,000.00 | $900.00 | $1,575.00 | $1,575.00 |
| $145,000 | $0.00 | $145,000.00 | $1,305.00 | $1,980.00 | $1,980.00 |
| $200,000 | $0.00 | $200,000.00 | $1,800.00 | $2,475.00 | $2,475.00 |
| $250,000 | $0.00 | $250,000.00 | $2,250.00 | $2,925.00 | $2,925.00 |
Form 8959 (Parts I through V) line-by-line worksheet
| Form 8959 line | Worksheet description | Amount |
|---|---|---|
| Part I, Line 1 / 4 | Total Medicare wages and tips (Form W-2, Box 5; combined on a joint return) | $325,000.00 |
| Part I, Line 5 | Filing-status threshold (Married filing jointly) | $250,000.00 |
| Part I, Line 6 | Medicare wages above threshold (Line 4 minus Line 5, minimum $0.00) | $75,000.00 |
| Part I, Line 7 | Additional Medicare Tax on Medicare wages (Line 6 × 0.009) | $675.00 |
| Part II, Line 8 | Self-employment income (Schedule SE, Part I, Line 6; losses entered as $0.00) | $0.00 |
| Part II, Line 11 | Self-employment threshold reduced by Line 4 Medicare wages (minimum $0.00) | $0.00 |
| Part II, Line 12 | Self-employment income above reduced threshold (Line 8 minus Line 11, minimum $0.00) | $0.00 |
| Part II, Line 13 | Additional Medicare Tax on self-employment income (Line 12 × 0.009) | $0.00 |
| Part III, Line 14 | Railroad Retirement Tax Act (RRTA) compensation and tips (Form W-2, Box 14) | $0.00 |
| Part III, Line 16 | RRTA compensation above separate filing-status threshold (Line 14 minus Line 15) | $0.00 |
| Part III, Line 17 | Additional Medicare Tax on RRTA compensation (Line 16 × 0.009) | $0.00 |
| Part IV, Line 18 | Total Additional Medicare Tax (Lines 7 + 13 + 17 -> Schedule 2, Line 11) | $675.00 |
| Part V, Line 19 | Total Medicare tax withheld on Form W-2, Box 6 (regular plus additional) | $4,712.50 |
| Part V, Line 21 | Regular Medicare tax withholding on Medicare wages (Line 20 × 0.0145) | $4,712.50 |
| Part V, Line 22 | Additional Medicare Tax withholding on Medicare wages (Line 19 minus Line 21) | $0.00 |
| Part V, Line 23 | Additional Medicare Tax withholding on RRTA compensation (Form W-2, Box 14) | $0.00 |
| Part V, Line 24 | Total Additional Medicare Tax withholding (Lines 22 + 23 -> Form 1040, Line 25c) | $0.00 |
Form 8959 Line 18 carries $675.00 to Schedule 2 Line 11 and Line 24 carries $0.00 to Form 1040 Line 25c, resulting in $675.00 of tax still owed.
Form 8959 tax, withholding, and net reconciliation across Medicare wage levels
| Your Medicare wages | Combined wages (Line 4) | Wages over threshold (Line 6) | Total tax (Line 18) | Withheld (Line 24) | Balance due | Credit | Effective rate |
|---|---|---|---|---|---|---|---|
| $100,000 | $275,000.00 | $25,000.00 | $225.00 | $0.00 | $225.00 | $0.00 | 0.08% |
| $150,000 | $325,000.00 | $75,000.00 | $675.00 | $0.00 | $675.00 | $0.00 | 0.21% |
| $175,000 | $350,000.00 | $100,000.00 | $900.00 | $0.00 | $900.00 | $0.00 | 0.26% |
| $200,000 | $375,000.00 | $125,000.00 | $1,125.00 | $0.00 | $1,125.00 | $0.00 | 0.30% |
| $225,000 | $400,000.00 | $150,000.00 | $1,350.00 | $225.00 | $1,125.00 | $0.00 | 0.34% |
| $250,000 | $425,000.00 | $175,000.00 | $1,575.00 | $450.00 | $1,125.00 | $0.00 | 0.37% |
| $300,000 | $475,000.00 | $225,000.00 | $2,025.00 | $900.00 | $1,125.00 | $0.00 | 0.43% |
| $400,000 | $575,000.00 | $325,000.00 | $2,925.00 | $1,800.00 | $1,125.00 | $0.00 | 0.51% |
| $500,000 | $675,000.00 | $425,000.00 | $3,825.00 | $2,700.00 | $1,125.00 | $0.00 | 0.57% |
As your Medicare wages rise from $100,000.00 to $500,000.00 (Married filing jointly), total Form 8959 tax moves from $225.00 to $3,825.00 while employer withholding moves from $0.00 to $2,700.00.
How the 0.9% Additional Medicare Tax and Form 8959 work
In a W-2 job, you and your boss each pay 1.45% for Medicare on all pay. There is no wage cap. Since 2013, an Additional Medicare Tax has applied to pay above a threshold. In the Instructions for Form 8959, the IRS explains that "A 0.9% Additional Medicare Tax applies to your Medicare wages, Railroad Retirement Tax Act (RRTA) compensation, and self-employment income above a threshold amount." As IRS Topic No. 560 notes, "There's no employer match for Additional Medicare tax." Compare regular check cuts in the take-home pay calculator or bonus checks in the bonus tax calculator.
Your tax bill on Form 8959 rests on your filing status. The surtax starts above $200,000 for most filers, $250,000 for joint filers, and $125,000 for married filing separately. Those dollar floors never change for inflation. A joint return counts both spouses' Medicare wages together. Tips from Form 4137 and wages from Form 8919 count as Medicare wages. Only your combined Medicare wages above your filing-status floor are taxed at 0.9%. Group-term life pay in Form W-2 Box 5 counts as Medicare wages; check it in the group-term life imputed income calculator.
Boss withholding uses a fixed rule for each worker that often misses your true tax. As the Instructions for Form 8959 state, "Your employer must withhold Additional Medicare Tax on wages it pays to you in excess of $200,000 for the calendar year, regardless of your filing status and regardless of wages or compensation paid by another employer." Under 26 CFR § 31.3102-4(a), a boss ignores a spouse's pay and second jobs. Two spouses or a two-job worker can owe hundreds of dollars with $0.00 withheld. By contrast, a one-earner joint filer paid between the withholding floor and the joint floor has tax held back even when owing $0.00.
How self-employment income (Part II) and RRTA compensation (Part III) coordinate with Medicare wages
When you earn both W-2 pay and freelance profit, you do not get two floors. On Form 8959 Part II, Line 8 takes your net business pay from Schedule SE Part I line 6 (see the self-employment tax calculator). As the Instructions for Form 8959 state, "If you have both wages and self-employment income, the threshold amount for applying Additional Medicare Tax on the self-employment income is reduced (but not below zero) by the total amount of Medicare wages received." You enter a business loss as $0.00 on Line 8, so it never cuts W-2 pay. Under 26 U.S.C. § 1401(b)(2)(B), Line 11 cuts your status floor by your FICA wages before Line 13 taxes the remaining self-employment excess.
Railroad Retirement Tax Act (RRTA) pay on Form W-2 Box 14 (or Form CT-2 line 2) sits in Part III (Lines 14 to 17). As IRS Topic No. 560 states, "Don't consider a self-employment loss for purposes of this tax. Compare railroad retirement (RRTA) compensation separately to the threshold." Thus, rail pay never joins FICA wages in Part I. It also never cuts your business floor on Line 11 in Part II.
How Form 8959 Part V reconciles Form W-2 Box 6 withholding with Schedule 2 and Form 1040
Employers do not put this surtax in a separate W-2 box for FICA workers. As the Instructions for Form 8959 note, "Both Medicare tax and Additional Medicare Tax withholding are reported together on Form W-2, box 6." Form 8959 Part V splits them up. Line 19 adds Box 6 across all your Forms W-2. Line 21 multiplies Line 1 pay by the regular Medicare rate. Line 22 subtracts Line 21 from Line 19 to find your surtax held back on wages. Adding any Box 14 rail surtax on Line 23 gives your total credit on Line 24.
Line 18 (Total Additional Medicare Tax) goes to Schedule 2 (Form 1040) line 11, which adds to your tax bill. Line 24 goes to Form 1040 line 25c along with your income tax held back. As the Instructions for Form 8959 state, "You can’t ask your employer to stop Additional Medicare Tax withholding if it is required to withhold it. If you don’t owe Additional Medicare Tax, you can claim a credit for any withheld Additional Medicare Tax against the total tax liability shown on your tax return by filing Form 8959." See how both lines settle in the federal income tax calculator.
Video walkthrough
A 3½-minute walkthrough of the pay the tax applies to, what your employer has to withhold, and where the amount goes on your return.
Read the transcript
How much do I owe?
0:00 Filing a joint return this year, your Additional Medicare Tax is $675.
0:06 Your employer withheld nothing from your pay, so the entire amount is still owed, at filing.
0:12 That tax is calculated from your pay and from your filing status.
0:16 A joint return's threshold is $250,000, and it covers both of you together.
0:22 Your pay and your spouse's pay add up to $325,000 a year, well over that line.
0:28 Neither person's pay, by itself, is over that line.
0:31 That line does not rise with inflation.
0:34 The threshold stays, year after year, at that same amount, unless Congress changes it.
Which pay gets the extra tax?
0:40 Consider how it works: the tax sits on the pay above the annual threshold.
0:45 So, it comes down to how much of your pay is above that $250,000 line this year.
0:52 Your pay above the line is taxed at 0.9%.
0:55 Only $75,000 of your combined pay is above that line, and all of it is taxed.
Why was nothing withheld?
1:02 Your employer withholds this tax on the wages it pays you above $200,000 for the year, whatever your filing status; your boss looks at one person at a time.
1:13 Hold your spouse's earnings exactly where they are, and move your own pay.
1:17 The tax line climbs at once, while your employer's line stays at zero until your own pay crosses the withholding limit.
1:25 Then both lines climb at the same rate, $1,125 apart.
1:30 Consider one earner instead of a couple.
1:33 That earner then pays no Additional Medicare Tax, but the boss withholds $450, and you can claim that $450 back on your return.
What does a side business change?
1:44 Now a business joins the same household, and your wages then change what it pays.
1:49 A business has its own separate threshold amount, and your household's combined pay has already used that threshold up.
1:57 So the business's threshold is already zero.
2:00 A business then brings in $100,000 of self-employment income each year, so $900 of tax lands on top of what your pay owes.
2:10 The IRS's instructions say the threshold falls by the Medicare wages you received, and stops at zero.
Where does the tax go on your return?
2:17 Now, the return itself.
2:19 The total tax sits on line 18 of Form 8959.
2:23 What your employer withheld sits on line 24.
2:27 One line raises your tax bill; the other lowers it.
2:30 The IRS's instructions say the amount your employer withheld goes on your income tax return, on the same line as your income tax withholding.
2:40 Your tax owed and the tax already paid meet on one page.
How do I check my own numbers?
2:44 Enter your own pay into the calculator.
2:47 As you type, the Additional Medicare Tax and the amount you still owe change.
2:52 The calculator works everything out, from the figures you enter, so, it follows your pay and your filing status.
2:59 Your $1,575 tax and what you owe sit side by side with any credit, so you can check that tax against the pay slip and the W-2.
3:09 The tax sits above your threshold.
3:12 Your employer withholds above $200,000.
3:15 You can check all of your own numbers at fastcalc.us.
Form 8959 (Parts I through V) calculation formulas
Filing-status threshold (26 U.S.C. § 3101(b)(2)): $250,000.00 Married Filing Jointly, $125,000.00 Married Filing Separately, $200,000.00 Single, Head of Household, or Qualifying Surviving Spouse Part I tax on Medicare wages (Form 8959 Line 7) = max($0.00, Combined W-2 Box 5 wages − Threshold) × 0.9% (0.009) Part II reduced SE threshold (Line 11) = max($0.00, Threshold − Combined Medicare wages); Part II tax (Line 13) = max($0.00, Schedule SE Line 6 income − Line 11) × 0.9% Part III tax on RRTA pay (Line 17) = max($0.00, RRTA Box 14 pay − Threshold) × 0.9%; Part IV total tax (Line 18) = Line 7 + Line 13 + Line 17 Part V mandatory employer withholding (26 CFR § 31.3102-4) = 0.9% of each employee's W-2 wages or RRTA pay above $200,000.00; Balance due = max($0.00, Line 18 − Line 24); Credit = max($0.00, Line 24 − Line 18)
Worked examples from IRS Form 8959 instructions and regulations
IRS Example 5 (Erin and Frank — Default joint return): Erin earns $150,000.00 and Frank earns $175,000.00 on a joint return ($0.00 business pay). Under [How It Works](#how-it-works), neither boss crosses the per-worker withholding floor, so Part V Line 24 is $0.00. Their bosses hold back only regular Medicare tax ($2,175.00 and $2,537.50, or $4,712.50 on Line 21). On Part I Line 4, their $325,000.00 total beats the joint floor by $75,000.00 on Line 6. That gives $675.00 on Line 7 and Line 18, leaving $675.00 due.
IRS Example 3 (Carl — Single) and Part II Example (Kathleen and Liam — Joint): Carl is Single with $130,000.00 of W-2 pay and $145,000.00 of Schedule SE line 6 pay. Under [Part II Coordination](#self-employment-rrta), Part I tax is $0.00 and boss withholding is $0.00. On Line 11, Carl's $130,000.00 of wages cuts his Single floor to $70,000.00. That leaves $75,000.00 of business pay on Line 12 and $675.00 of tax on Line 13. Likewise, Kathleen ($130,000.00 wages) and Liam ($140,000.00 business pay) cut their joint floor to $120,000.00 on Line 11. They owe the surtax on the remaining $20,000.00 for $180.00.
IRS Example 4 (Don — Separate) and 26 CFR § 31.3102-4(a) Example (H and I — Joint): Don files separately with $200,000.00 of wages and $150,000.00 of business pay. His boss holds back $0.00 because his pay does not beat the employer trigger ([How It Works](#how-it-works)). Above the Separate floor, Don owes $675.00 on $75,000.00 of wages on Line 7. Because wages cut his Line 11 floor to $0.00, he also owes $1,350.00 on all $150,000.00 of business pay, for $2,025.00 total. For joint spouses H ($100,000.00) and I ($300,000.00), $400,000.00 total leaves $150,000.00 taxable for $1,350.00. Spouse I's boss holds back $900.00 on the $100,000.00 over the employer trigger, leaving $450.00 due.
One-earner joint credit ($230,000.00 wages, $0.00 spouse wages) and IRS Examples 6 & 7 (RRTA): Under [Part V Reconciliation](#withholding-reconciliation), the boss must hold back the surtax on the $30,000.00 above the employer trigger ($270.00 on Line 24). Because $230,000.00 sits below the joint floor, Line 18 tax is $0.00. Filing Form 8959 claims a $270.00 credit on Form 1040 line 25c. In Examples 6 and 7, George ($190,000.00 wages) and Helen ($150,000.00 RRTA) owe $0.00. Ishmael ($160,000.00 SE) and Judy ($140,000.00 RRTA) also owe $0.00 because Part III tests rail pay on its own.
Assumptions, threshold limits, and scope
- Computes Parts I to V in whole cents (half-up rounding) across all 5 statuses using the fixed statutory floors in 26 U.S.C. § 3101(b)(2).
- In 'Estimate from wages' mode, applies 26 CFR § 31.3102-4(a) assuming your pay, your spouse's pay, and any rail pay each come from one boss. If you switched jobs or held two W-2 jobs, pick 'Enter the Additional Medicare Tax withheld'.
- Treats the self-employment field as Schedule SE Part I line 6 net pay (92.35% of profit; $0.00 if under $400.00 or a loss). To start from raw Schedule C profit, use the self-employment tax calculator first.
- Covers only the Form 8959 surtax and its Box 6 or Box 14 credits. Under the IRS FAQs, the 3.8% Net Investment Income Tax in 26 U.S.C. § 1411 never applies to FICA wages, RRTA pay, or self-employment income.
These figures are estimates for learning and planning, not financial, tax, legal or investment advice. Terms of use.
What to do with your Form 8959 numbers
Check if you must attach Form 8959 to your return. File it if any single W-2 Box 5 (or Box 14 rail pay) beats the employer trigger ([How It Works](#how-it-works)). Also file it if total pay beats your status floor, or if any surtax is owed or held back.
If you have a balance due, pay it before year-end to avoid a charge under 26 U.S.C. § 6654. You cannot ask for extra Medicare withholding. Instead, add income tax pay cuts on Form W-4 Step 4(c) in the federal paycheck withholding calculator.
If you pay by quarter or earn freelance profit, fold the balance into your Form 1040-ES vouchers in the quarterly estimated tax calculator. No penalty applies if your net Form 1040 balance after credits stays under $1,000.00. Check late charges in the IRS penalty and interest calculator.
Additional Medicare Tax and Form 8959 questions
What are the income thresholds for the 0.9% Additional Medicare Tax?
Under 26 U.S.C. § 3101(b)(2), the floors are set by filing status for Joint, Separate, and all other filers. Because Congress did not index them for inflation, those dollar amounts stay the same every tax year.
Why did neither employer withhold the tax when my spouse and I owe it on a joint return?
Under 26 CFR § 31.3102-4(a), a boss holds back the surtax only after paying one worker past the employer trigger in a year ([How It Works](#how-it-works)). When two spouses earn below that trigger alone, neither boss holds back a cent. Yet their combined pay can still beat the joint floor ([Example 1](#example)).
Can I ask my employer to stop withholding Additional Medicare Tax if our joint income is under $250,000?
No. Under 26 CFR § 31.3102-4(a), your boss must hold back the surtax once your own pay crosses the employer trigger ([Part V Reconciliation](#withholding-reconciliation)). A boss cannot stop on request. You get the extra money back by filing Form 8959 and claiming the Line 24 credit on Form 1040 line 25c.
How is Additional Medicare Tax calculated when I have both W-2 wages and self-employment income?
Form 8959 Part II cuts your filing-status floor (not below $0.00) by your Line 4 Medicare wages ([Part II Coordination](#self-employment-rrta)). You then test your Schedule SE line 6 pay against the remaining room. That stops you from using the floor twice across W-2 and business pay.
Does Railroad Retirement (RRTA) compensation combine with W-2 Medicare wages or self-employment income?
No. On Form 8959 Part III, RRTA pay in Form W-2 Box 14 is tested on its own against the full floor for your status ([Part II Coordination](#self-employment-rrta)). It never joins FICA wages or cuts your business floor on Line 11.
Does the 0.9% Additional Medicare Tax overlap with the 3.8% Net Investment Income Tax?
No. Under 26 U.S.C. § 1411 and the IRS FAQs, the investment surtax applies only to passive and investment income ([Assumptions](#assumptions)). It never applies to wages, RRTA pay, or self-employment income.
Sources
- IRS, Form 8959 (2025), Additional Medicare Tax (current version)
- IRS, Instructions for Form 8959 (2025), Additional Medicare Tax (page reviewed Feb 2, 2026)
- IRS, Topic No. 560, Additional Medicare Tax (page reviewed Oct 9, 2026)
- IRS, Topic No. 751, Social Security and Medicare withholding rates (page reviewed Sep 24, 2026)
- IRS, Questions and answers for the Additional Medicare Tax (page reviewed Oct 25, 2026)
- 26 U.S.C. 3101, rate of Social Security and Medicare taxes (Cornell LII text) (current version)
- 26 U.S.C. 1401, rate of tax on self-employment income (Cornell LII text) (current version)
- 26 CFR 31.3101-2, rates and computation of hospital insurance taxes (eCFR) (current version)
- 26 CFR 31.3102-4, special rules regarding Additional Medicare Tax (eCFR) (current version)
- IRS, Publication 15 (2026), Employer’s Tax Guide (page reviewed Apr 30, 2026)
- IRS, Form W-4 (2026), Employee's Withholding Certificate (page modified Dec 11, 2025)
- IRS, Form 1040-ES (2026), Estimated Tax for Individuals (form dated Feb 12, 2026)
- Social Security Administration, Contribution and Benefit Base (current version)
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