Take-home pay: FICA + Additional Medicare Tax (employee withholding)
This calculator estimates the employee payroll taxes withheld from a paycheck under FICA:
Social Security (OASDI) and Medicare (HI), plus Additional Medicare Tax when applicable.
It is intended for paycheck-level withholding estimates and simple “take-home after payroll tax” planning.
What this calculator includes
- Social Security tax (employee share): 6.2% on wages up to the year’s wage base.
- Medicare tax (employee share): 1.45% on all Medicare wages (no annual wage base limit).
- Additional Medicare Tax: 0.9% on Medicare wages above the applicable threshold (withholding rules differ from final liability).
- Net after FICA: gross pay minus the computed payroll taxes (and optionally minus federal income tax withholding if you provide it).
What this calculator does not include
- Self-employment (SE) tax (separate topic; different rules and rates).
- State/local taxes, retirement contributions, health premiums, garnishments, or other paycheck deductions.
- Full-year tax return logic (Form 1040); this tool focuses on payroll taxes and basic take-home effects.
Important definitions and assumptions
Payroll tax computations depend on the definition of wages subject to FICA. Many “pre-tax” deductions reduce
federal income tax wages but may or may not reduce FICA wages depending on the plan type.
For simplicity, this calculator treats the entered gross pay and year-to-date wages as the amounts
already measured on the same FICA wage basis used for withholding.
Rates and wage base
Social Security and Medicare payroll tax rates (employee share) are commonly summarized by the IRS. The Social Security tax
applies only up to the year’s maximum taxable earnings (wage base), while Medicare has no wage cap.
The Social Security wage base is published annually by SSA (often called the “contribution and benefit base”).
This calculator stores the wage base as a tax-year constant, which you should update each year.
Social Security tax on a paycheck (with wage base)
Let:
g = gross pay for this period,
y = year-to-date wages before this paycheck,
B = Social Security wage base for the selected tax year.
Only the portion of this paycheck that falls below the remaining wage base is subject to Social Security tax.
\[
\begin{aligned}
\text{Remaining wage base} &= \max(0,\; B - y) \\
\text{SS-taxable this paycheck} &= \max\!\big(0,\; \min(g,\; B - y)\big) \\
\text{Social Security withheld} &= 0.062 \cdot \text{SS-taxable this paycheck}
\end{aligned}
\]
If \(y \ge B\), then \(\text{SS-taxable this paycheck} = 0\) and no additional Social Security tax is withheld for the rest of the year
(but Medicare still applies).
Medicare tax on a paycheck
Medicare withholding applies to all Medicare wages (no annual wage base limit):
\[
\begin{aligned}
\text{Medicare withheld} &= 0.0145 \cdot g
\end{aligned}
\]
Additional Medicare Tax: withholding vs final liability
Additional Medicare Tax is an extra 0.9% on Medicare wages above a threshold. Two concepts matter:
(1) the employer withholding rule, and (2) the filing-status threshold used to compute your final liability on Form 8959.
-
Employer withholding rule: employers generally begin withholding Additional Medicare Tax once an employee’s wages exceed
$200,000 in a calendar year (regardless of filing status).
-
Filing-status thresholds (final liability concept):
\( \$250{,}000 \) (Married filing jointly),
\( \$125{,}000 \) (Married filing separately),
\( \$200{,}000 \) (Single, Head of household, Qualifying surviving spouse).
This calculator can show Additional Medicare tax using either threshold mode. The two results can differ because withholding rules
are designed for payroll administration, while the final threshold depends on your total annual income and filing status.
Additional Medicare tax attributable to this paycheck
Let \(\tau\) be the selected threshold (either the employer rule \(200{,}000\) or the filing-status threshold).
The portion of this paycheck above the threshold is the increase in “wages above \(\tau\)” caused by this pay period.
\[
\begin{aligned}
\text{Above-threshold before} &= \max(0,\; y - \tau) \\
\text{Above-threshold after} &= \max(0,\; (y + g) - \tau) \\
\text{Add'l Medicare taxable this paycheck} &= \text{Above-threshold after} - \text{Above-threshold before} \\
\text{Add'l Medicare withheld} &= 0.009 \cdot \text{Add'l Medicare taxable this paycheck}
\end{aligned}
\]
If your year-to-date wages are below \(\tau\), you may see Additional Medicare begin only in the paycheck where \((y+g)\) crosses \(\tau\),
and then continue for later paychecks.
Net pay after payroll taxes (and optional federal withholding)
This calculator reports take-home after these payroll taxes, and optionally subtracts an entered federal income tax withholding amount
(useful if you pair it with a separate W-4 withholding estimator).
\[
\begin{aligned}
\text{FICA total} &= \text{Social Security} + \text{Medicare} + \text{Add'l Medicare} \\
\text{Net after FICA} &= g - \text{FICA total} \\
\text{Net after FICA and federal (optional)} &= g - \text{FICA total} - w_{\text{fed}}
\end{aligned}
\]
How to keep this calculator updated each year
- Update the Social Security wage base \(B\) from SSA’s published annual value.
- Verify the current withholding rates for Social Security and Medicare in IRS guidance.
- Confirm Additional Medicare guidance (thresholds and employer withholding behavior) with IRS Form 8959 resources.
Primary references
IRS Topic 751 (Social Security and Medicare withholding overview):
https://www.irs.gov/taxtopics/tc751
SSA Contribution and Benefit Base (maximum taxable earnings / wage base):
https://www.ssa.gov/oact/cola/cbb.html
SSA FAQ (maximum taxable earnings explanation):
https://faq.ssa.gov/en-us/Topic/article/KA-02341
IRS “About Form 8959” (Additional Medicare Tax hub):
https://www.irs.gov/forms-pubs/about-form-8959
IRS page with related items including Form 8959 (as provided):
https://www.irs.gov/f1040es
