US FICA Tax: what the Wage101 calculator includes

The three employee FICA components do different jobs

FICA is not one flat percentage applied to every dollar of wages. Social Security stops applying after its annual wage base is used, regular Medicare has no wage cap in this bounded model, and Additional Medicare withholding depends on where employer year-to-date Medicare wages cross its withholding threshold.

Bounded 2026 employee FICA components
Component	Employee rate	Cap or threshold	Input needed	Result meaning
Social Security	6.2%	$184,500 calendar-year wage base	Current FICA wages and prior Social Security wages	Tax on this payment’s wages that remain below the wage base
Medicare	1.45%	No wage cap	Current FICA wages	Regular employee Medicare withholding for this payment
Additional Medicare	0.9%	$200,000 employer withholding threshold	Current FICA wages and prior Medicare wages	Extra amount the employer withholds on wages above the threshold

Enter the two year-to-date wage amounts separately

Enter Social Security wages and Medicare wages accumulated with the employer immediately before the current payment. They are separate inputs because the Social Security wage base and Additional Medicare withholding threshold are separate tests.

When prior Social Security wages plus the current payment cross $184,500, only the part of the payment still inside the wage base receives the 6.2% charge. Medicare continues on the payment, while the additional 0.9% applies only to the newly crossed employer-threshold wages.

A wage base is not an amount withheld

Social Security wages and Medicare wages are earnings records used as calculation bases. Social Security, Medicare and Additional Medicare withholding are money amounts calculated from the applicable base and threshold. Compare a wage-base line with the matching wage record, and compare a withholding line with the matching calculated amount; do not compare wage dollars with tax dollars as though they were the same measure.

Federal income-tax withholding is a separate payroll collection under its own inputs and rules. It is not part of the Wage101 FICA result, and neither federal income-tax withholding nor FICA withholding by itself establishes final filing liability or a refund.

Keep federal wage bases and withholding records separate
Record	What it represents	What it does not represent
Social Security wages	Earnings recorded for the Social Security calculation and annual wage-base test	Social Security tax withheld or federal income-tax withholding
Medicare wages	Earnings recorded for regular and Additional Medicare withholding tests	The Social Security wage base or the amount of Medicare tax withheld
Employee FICA withheld	The separately calculated Social Security, Medicare and Additional Medicare amounts	Federal income-tax withholding, complete take-home pay or final liability
Federal income tax withheld	A separate payroll collection shown on the employer record	A FICA result, final federal income-tax liability or a refund estimate

A $5,000 payment produces $382.50 in the calculator example

The production example starts with a $5,000 current payment, $50,000 of prior Social Security wages, $50,000 of prior Medicare wages, and a $500 pretax 401(k) contribution shown for wage-basis context.

calculator-aligned FICA example in USD per payment
Step	Calculation	Amount
Social Security	$5,000 × 6.2%	$310.00
Medicare	$5,000 × 1.45%	$72.50
Additional Medicare	No employer-threshold crossing	$0.00
Total employee FICA	$310.00 + $72.50 + $0.00	$382.50

The 401(k) field is context, not a FICA reduction

In this bounded tool, FICA wages equal gross wages. The $500 pretax 401(k) input reduces only the separately displayed federal income-tax wage basis before other adjustments; it does not reduce the $5,000 FICA wage input or the $382.50 result.

That is a statement about this tool’s reviewed fixture, not general retirement-plan or tax advice. Verify the actual payroll treatment when a plan, payment, or correction falls outside the model.

Use the result to check components, not final liability

A payroll or offer comparison can use the three output lines to identify which component changed and whether the entered year-to-date wages explain it. The Additional Medicare line shows employer withholding under the $200,000 trigger; filing status and final Additional Medicare liability are separate questions this model does not answer.

A late-year zero Social Security amount can be consistent with the annual wage base while regular Medicare continues. Differences involving multiple employers, refunds, exemptions, or corrections require payroll or tax review.

What the FICA estimate deliberately leaves out

The evidence boundary covers the four reviewed 2026 employee FICA rules and the production formula. It does not turn this article into a complete paycheck calculator.

No federal, state, or local income-tax withholding; filing status; or final tax liability.
No employer FICA, self-employment tax, worker classification, or exemption decision.
No benefits, payroll corrections, refunds, or multi-employer reconciliation.
No complete take-home-pay calculation or personalised tax advice.
Review the official IRS Publication 15 source and the calculator methodology when rates, wage bases, or the calendar year change.