Methodology & Data Sources

What the Calculator Computes

The PlainSalary calculator estimates US federal income tax, state income tax, and FICA / SECA payroll tax for tax year 2026. Inputs: gross annual income, filing status (single, married jointly, married separately, head of household), and US state. Outputs: federal income tax, state income tax, FICA, total tax, take-home pay, effective rate, federal marginal rate, state marginal rate, and combined top marginal rate.

Data Sources

All bracket schedules and rates trace back to primary, authoritative US government sources:

Federal Income Tax Brackets

IRS Revenue Procedure 2025-32 - the official 2026 inflation-adjustment notice published October 2025. Provides the seven marginal brackets for each of four filing statuses, the 2026 standard deduction, AMT exemption amounts, and long-term capital gains thresholds. Source URL: irs.gov/pub/irs-drop/rp-25-32.pdf.
Source: IRS Revenue Procedure 2025-32, 2026 federal inflation adjustments.

State Income Tax Brackets and Rates

Each US state Department of Revenue publishes its own bracket schedule. We verified each state's 2026 rate effective January 1, 2026 against the official DOR notices. As a cross-check we also reference the Tax Foundation's State Individual Income Tax Rates and Brackets, 2026 aggregator (taxfoundation.org), which compiles all 50 states plus DC.
Source: State Departments of Revenue 2026 personal-income-tax publications, cross-checked against Tax Foundation State Individual Income Tax Rates and Brackets 2026.

FICA / Medicare

Rates and the 2026 Social Security wage base ($184,500) come from the SSA Fact Sheet 2026 Social Security Changes (ssa.gov). The additional Medicare 0.9% surcharge thresholds ($200,000 single / $250,000 married jointly) are statutory and frozen since 2013, they are not inflation-indexed.
Source: SSA Fact Sheet 2026 Social Security Changes; Internal Revenue Code §1411 (Affordable Care Act 2010).

Computation Pipeline

The calculator runs entirely in the user's browser. No input is transmitted to any server. The computation order:

  1. Apply standard deduction (if user opts in). Gross income minus standard deduction = taxable income.
  2. Federal income tax. Walk the 2026 marginal brackets for the chosen filing status. For each bracket where taxable income exceeds the bracket low, compute (min(taxable, bracket_high) − bracket_low) × marginal_rate. Sum all bracket contributions.
  3. State income tax. For states with detailed bracket schedules in our database (CA, NY, MA, NJ, IL, PA, GA, CO, NC), apply the same progressive walk algorithm. For other progressive states, approximate with the top marginal rate × taxable income (an upper-bound, see "Limitations" below). For flat-tax states, multiply taxable income by the flat rate. For no-income-tax states, state tax = 0.
  4. FICA / SECA. Social Security: min(gross_wage, 184500) × 6.2% (employee) or 12.4% (self-employed). Medicare: gross_wage × 1.45% (employee) or 2.9% (self-employed). Additional Medicare: max(0, gross_wage − threshold) × 0.9%. Sum.
  5. Total tax. Federal + state + FICA. Take-home. Gross minus total tax. Effective rate. Total tax ÷ gross.

Worked example: $80,000 single filer, California, standard deduction

Step-by-step bracket walk to demonstrate the algorithm end-to-end:

  1. Taxable income: $80,000 − $16,100 standard deduction = $63,900.
  2. Federal tax (2026 single brackets, walking each tier in order):
    • $12,400 × 10% = $1,240.00
    • ($50,400 − $12,400) × 12% = $38,000 × 12% = $4,560.00
    • ($63,900 − $50,400) × 22% = $13,500 × 22% = $2,970.00
    • Total federal = $8,770.00
  3. California state tax (2026 single, walking the progressive bracket schedule on $63,900 taxable): roughly $2,496 with the standard CA progressive brackets.
  4. FICA on $80,000 gross wages: Social Security $80,000 × 6.2% = $4,960; Medicare $80,000 × 1.45% = $1,160; total $6,120.
  5. Total tax: $8,770 + $2,496 + $6,120 = $17,386. Take-home: $80,000 − $17,386 = $62,614. Effective rate: 21.73% on gross.

The marginal rate for the next dollar of income at this tier is 22% federal + the CA bracket rate at $63.9K. Punch the same inputs into the calculator to verify (figures match within $1 rounding).

Limitations

The calculator estimates the three core tax layers using gross income and standard deduction. It does not account for:

  • Itemized deductions beyond the standard deduction - mortgage interest, state and local taxes (SALT, capped at $40,000 for 2025-2029), charitable contributions, large medical expenses
  • Above-the-line adjustments - traditional IRA, HSA, student loan interest, half-SECA deduction, self-employed health insurance
  • Tax credits - Child Tax Credit (refundable up to $1,700/child in 2026), Earned Income Tax Credit, Child & Dependent Care Credit, education credits (American Opportunity, Lifetime Learning), foreign tax credit, residential energy credits
  • Alternative Minimum Tax (AMT) - narrowly applies after 2017 TCJA but still relevant for ISO exercisers and very-high-income filers
  • Capital gains preferential rates - long-term gains taxed at 0%, 15%, 20% federal plus 3.8% NIIT above $200K/$250K thresholds
  • State-specific deductions and credits - varies by state
  • Local income taxes - NYC city tax (3-3.876%), some Pennsylvania municipalities, several Indiana and Maryland counties, school-district income taxes in Ohio
  • For states without detailed brackets in our DB (19 progressive states beyond the 9 with detailed schedules), we approximate with the top marginal rate, which over-states tax at lower incomes. Use the per-state page for the precise schedule.

Update Schedule

  • Federal brackets: refreshed within 2 weeks of each year's IRS Revenue Procedure publication (typically mid-November)
  • FICA wage base: refreshed within 2 weeks of SSA October announcement
  • State brackets: refreshed through Q4 of the preceding year for January-1 effective changes; mid-year changes (rare) refreshed within 2 weeks

Verification

For each major data refresh we independently re-derive a sample of bracket-schedule outputs against the official source PDF. Any computational discrepancy blocks the release. We publish the data update history at our about page.

Open Methodology

The bracket data is shipped to your browser as a static JSON snapshot. The math is plain JavaScript, no server, no opaque computation. You can read the formulas in the page source. If you find a discrepancy with the official IRS or state DOR schedule, please email hello@plainsalary.com with the page URL, the input values, and the source you compared against.

Disclaimer

This calculator is for informational purposes only and does not provide tax, financial, or legal advice. Tax law is complex; individual circumstances vary; the calculator excludes deductions, credits, AMT, capital gains preferential rates, and local taxes. For your actual filing, use commercial tax preparation software or a qualified tax professional.