Marginal Tax Rate Calculator
This calculator provides a practical, combined estimate of the marginal tax rate that applies to incremental income by summing your federal, state, and payroll tax components. It is intended for quick scenario analysis (for example, evaluating the after-tax value of a bonus or overtime).
The result is an estimate only. It does not replace professional tax advice or a full tax return computation. Read the methodology and accuracy notes below before using results for financial decisions.
Governance
Record d0d0e2f3d272 • Reviewed by Fidamen Standards Committee
Inputs
Results
Combined marginal tax rate
31.65%
Sum of component rates (%)
3165.00%
Estimated tax on additional income
$316.50
Estimated after-tax additional income
$683.50
| Output | Value | Unit |
|---|---|---|
| Combined marginal tax rate | 31.65% | — |
| Sum of component rates (%) | 3165.00% | — |
| Estimated tax on additional income | $316.50 | — |
| Estimated after-tax additional income | $683.50 | — |
Visualization
Methodology
User-entered component rates (federal, state, payroll) are summed to produce a combined marginal rate. This approach reflects how an additional dollar of income is typically taxed across overlapping tax systems when each component applies to that same incremental dollar.
The calculator treats inputs as percentages on the marginal dollar. The payroll tax field should reflect the marginal payroll burden you personally pay on the next dollar earned (for example, employee FICA share ≈ 7.65% or self-employed combined ≈ 15.3%).
Estimates are bounded to the mathematically meaningful range (0%–100%). For precision-sensitive use cases (complex deductions, phaseouts, AMT, ACA surtaxes), run a full tax simulation or consult a tax professional.
Worked examples
Example 1: Federal 24%, State 5%, Payroll 7.65% on an extra $1,000 → Combined ≈ 36.65%, Tax ≈ $366.50, After-tax ≈ $633.50.
Example 2: Federal 37%, State 0%, Payroll 0% on an extra $10,000 → Combined = 37%, Tax = $3,700, After-tax = $6,300.
F.A.Q.
Does this calculator compute my federal tax return or effective tax rate?
No. This tool estimates the marginal tax rate on additional income. Effective tax rate (total tax paid divided by total income) and full return calculations require comprehensive inputs—deductions, credits, capital gains, AMT, and other rules—and are beyond this quick estimator.
How should I set the payroll tax rate field?
Enter the marginal payroll taxes you personally pay on the next dollar. Employees typically use employee FICA share (about 7.65%); self-employed individuals typically include the employer and employee share (about 15.3%) unless they plan to deduct the employer-equivalent portion. Adjust if you are subject to Medicare surtax or Social Security wage base limits.
Will state tax always apply to the same marginal dollar?
State tax rules vary and some states have bracket structures and phaseouts. This calculator assumes any entered state rate applies to the marginal dollar. For detailed state-specific modeling, use a jurisdiction-specific tax calculator or professional software.
What are the tool’s limitations?
This is an estimate and does not model complex interactions such as tax credits, itemized deductions, AMT, net investment income tax, or benefit phaseouts. Results should be used for illustrative, planning, or educational purposes only.
Sources & citations
- Internal Revenue Service (IRS) - official site — https://www.irs.gov/
- Social Security Administration (FICA rates & limits) — https://www.ssa.gov/
- NIST Cybersecurity Framework (data protection best practices) — https://www.nist.gov/cyberframework
- ISO/IEC 27001 Information Security Management — https://www.iso.org/isoiec-27001-information-security.html
- IEEE - professional and technical standards organization — https://www.ieee.org/
- IRS Publication 15-T — Federal Income Tax Withholding Methods — https://www.irs.gov/publications/p15t
- IRS Publication 505 — Tax Withholding and Estimated Tax — https://www.irs.gov/publications/p505
- IRS Tax Withholding Estimator — https://www.irs.gov/individuals/tax-withholding-estimator
Further resources
Versioning & Change Control
Audit record (versions, QA runs, reviewer sign-off, and evidence).
Record ID: d0d0e2f3d272What changed (latest)
v1.0.0 • 2025-11-18 • MINOR
Initial publication and governance baseline.
Why: Published with reviewed formulas, unit definitions, and UX controls.
Public QA status
PASS — golden 25 + edge 120
Last run: 2026-01-23 • Run: golden-edge-2026-01-23
Versioning & Change Control
Audit record (versions, QA runs, reviewer sign-off, and evidence).
What changed (latest)
v1.0.0 • 2025-11-18 • MINOR
Initial publication and governance baseline.
Why: Published with reviewed formulas, unit definitions, and UX controls.
Public QA status
PASS — golden 25 + edge 120
Last run: 2026-01-23 • Run: golden-edge-2026-01-23
Engine
v1.0.0
Data
Baseline (no external datasets)
Content
v1.0.0
UI
v1.0.0
Governance
Last updated: Nov 18, 2025
Reviewed by: Fidamen Standards Committee (Review board)
Credentials: Internal QA
Risk level: low
Reviewer profile (entity)
Fidamen Standards Committee
Review board
Internal QA
Entity ID: https://fidamen.com/reviewers/fidamen-standards-committee#person
Semantic versioning
- MAJOR: Calculation outputs can change for the same inputs (formula, rounding policy, assumptions).
- MINOR: New features or fields that do not change existing outputs for the same inputs.
- PATCH: Bug fixes, copy edits, or accessibility changes that do not change intended outputs except for previously incorrect cases.
Review protocol
- Verify formulas and unit definitions against primary standards or datasets.
- Run golden-case regression suite and edge-case suite.
- Record reviewer sign-off with credentials and scope.
- Document assumptions, limitations, and jurisdiction applicability.
Assumptions & limitations
- Uses exact unit definitions from the Fidamen conversion library.
- Internal calculations use double precision; display rounding follows the unit's configured decimal places.
- Not a substitute for calibrated instruments in regulated contexts.
- Jurisdiction-specific rules may require official guidance.
Change log
v1.0.0 • 2025-11-18 • MINOR
Initial publication and governance baseline.
Why: Published with reviewed formulas, unit definitions, and UX controls.
Areas: engine, content, ui • Reviewer: Fidamen Standards Committee • Entry ID: 35247e5c1341