Our Calculation Methodology
All calculations on US Financial Calculators are estimates based on publicly available US tax law and standard financial formulas. We document every assumption, data source, and known limitation so you can make informed use of our tools.
Data Sources
Our federal tax calculations use data published annually by the Internal Revenue Service (IRS), including:
- IRS Revenue Procedure for inflation-adjusted tax brackets (Rev. Proc. 2024-40 for tax year 2025; Rev. Proc. 2025-xx for tax year 2026)
- IRS Publication 15-T for paycheck withholding tables and supplemental wage rates
- Social Security Administration announcement for the annual FICA wage base
- IRS Publication 501 for standard deduction amounts and filing status rules
- IRS Publication 946 and topic pages for depreciation (where applicable)
State tax data is sourced from each state's Department of Revenue or equivalent agency. We use official published bracket tables, standard deduction amounts, and personal exemption values for each state.
Mortgage and loan calculations use the standard amortization formula. Property tax rate data is sourced from the Tax Foundation's annual State-Local Tax Burden Rankings report and ATTOM Data Solutions' property tax analysis. Median home prices are sourced from Zillow Research and the National Association of Realtors.
Federal Income Tax (2026)
We apply the progressive bracket method. Taxable income equals gross income minus the standard deduction (or itemized deductions if specified) minus pre-tax contributions. Tax is computed by applying each bracket rate only to the income within that bracket's range and summing the results.
The 2026 federal income tax brackets are:
| Rate | Single Filers | Married Filing Jointly | Head of Household |
|---|---|---|---|
| 10% | $0 – $11,925 | $0 – $23,850 | $0 – $17,000 |
| 12% | $11,925 – $48,475 | $23,850 – $96,950 | $17,000 – $64,850 |
| 22% | $48,475 – $103,350 | $96,950 – $206,700 | $64,850 – $103,350 |
| 24% | $103,350 – $197,300 | $206,700 – $394,600 | $103,350 – $197,300 |
| 32% | $197,300 – $250,525 | $394,600 – $501,050 | $197,300 – $250,500 |
| 35% | $250,525 – $626,350 | $501,050 – $751,600 | $250,500 – $626,350 |
| 37% | Over $626,350 | Over $751,600 | Over $626,350 |
2026 Standard Deduction: $15,000 (Single) · $30,000 (Married Filing Jointly) · $22,500 (Head of Household).
FICA Taxes (Social Security & Medicare) — 2026
| Tax | Employee Rate | Employer Rate | 2026 Wage Limit |
|---|---|---|---|
| Social Security | 6.2% | 6.2% | $176,100 |
| Medicare | 1.45% | 1.45% | No limit |
| Additional Medicare | 0.9% | None | >$200k (single) / >$250k (MFJ) |
FICA taxes are calculated on gross wages before the federal standard deduction. Pre-tax 401(k) contributions reduce income tax but not FICA; Section 125 health insurance contributions reduce both federal income tax and FICA.
State Income Taxes
We currently support 5 states. Each uses the state's officially published bracket structure and deduction rules:
| State | Tax Structure | Rate / Top Rate | Standard Deduction (Single) | Personal Exemption (Single) |
|---|---|---|---|---|
| California | Progressive | 1%–13.3% | $5,202 | $144 |
| Texas | None | 0% | N/A | N/A |
| Florida | None | 0% | N/A | N/A |
| New York | Progressive | 4%–10.9% | $8,000 | None |
| Illinois | Flat | 4.95% | None | $2,425 |
State taxable income is calculated separately from federal taxable income. State standard deductions and exemptions differ from the federal amounts.
Mortgage & Loan Calculations
Amortization Formula
Monthly principal and interest payments use the standard fixed-rate amortization formula:
- M = monthly payment
- P = loan principal (home price minus down payment)
- r = monthly interest rate (annual rate ÷ 12)
- n = total number of monthly payments (years × 12)
This formula produces equal monthly payments over the loan term, with the interest/principal split shifting over time (amortization).
PMI
We estimate Private Mortgage Insurance (PMI) at 0.5% of the loan amount annually when the down payment is less than 20% of the purchase price. Actual PMI rates range from approximately 0.2% to 2.0%.
Default Assumptions
- Filing status default: Single filer (can be changed in all calculators)
- Pre-tax deductions default: $0 (user can enter 401k, HSA, health insurance amounts)
- State default: No state tax (user selects their state)
- Standard deduction: Always applied unless user specifies pre-tax deductions that exceed it
- Mortgage default interest rate: 7.0% (current market rate placeholder — update to current rate)
- Homeowner's insurance: $1,800/year default (user can change)
- Pay frequency default: Bi-weekly (26 periods/year)
- Tax year default: 2026 (users can switch to prior years for comparison)
What Is NOT Included
Our calculators intentionally omit certain factors to keep them simple and widely applicable:
- Tax credits — Child Tax Credit, EITC, education credits, energy credits, foreign tax credits
- Alternative Minimum Tax (AMT) — affects some high-income filers with certain deductions
- Net Investment Income Tax (NIIT) — 3.8% surtax on investment income above income thresholds
- Itemized deductions — mortgage interest, charitable contributions, medical expenses, SALT deduction
- Local/city income taxes — NYC, Chicago, etc.
- State-specific credits and phase-outs
- Self-employment taxes — calculated separately in our dedicated SE Tax calculator
- Variable-rate loan products — our calculators assume fixed rates
Data Currency
We review and update all calculators in January of each year to reflect changes effective for the new tax year. The site uses a server-side tax engine so all calculations automatically use the selected year's published rates.
Current default year: 2026. Users can switch to any year from 2020–2026 using the Tax Year Selector on each calculator page. If you believe a rate is outdated or incorrect, please contact us.
Not Financial Advice
Results Are Estimates — Not Advice
All calculator results are estimates based on simplified assumptions and the exclusions documented above. Your actual tax liability, take-home pay, loan costs, and savings outcomes may differ. Tax situations vary significantly based on individual circumstances. These tools are for educational and planning purposes only. They do not constitute tax, financial, investment, or legal advice. Always consult a qualified CPA, CFP, or attorney for major financial decisions.