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How our calculators work

We want you to understand exactly where our numbers come from and what assumptions we make. This page explains our data sources, formulas, and limitations.

Last reviewed May 2026 · USAFinCalc Editorial Team

Data sources

Every number in our calculators comes from a public government source. We don't estimate figures or use third-party data when the official source is available.

Internal Revenue Service (IRS)

Federal income tax brackets, standard deductions, FICA rates, 401k limits, and IRA contribution limits. Updated annually via Revenue Procedures.

irs.gov — Rev. Proc. 2025-28 →

Bureau of Labor Statistics (BLS)

Consumer Price Index data for the inflation calculator. Historical CPI data from 1913 to present.

bls.gov/cpi →

Social Security Administration (SSA)

AIME/PIA formula, bend points, and full retirement age tables for the Social Security calculator.

ssa.gov/oact →

State revenue departments

State income tax rates and brackets sourced from each state's department of revenue. Updated when states publish new rates.

Calculator assumptions

Every calculator simplifies reality to some degree — that's what makes them fast and useful. Here's what each one assumes, so you know where the results might diverge from your actual situation.

Salary & Tax Calculator

Standard deduction only. We apply the standard deduction. If you itemize, your actual tax will differ.

W-2 income only. Results assume all income is from wages. Self-employment, investment income, and rental income are not included.

No credits applied. Child tax credit, EITC, education credits, and other credits are not factored in. Your actual tax liability will likely be lower.

Mortgage Calculator

Fixed-rate mortgage. All calculations assume a fixed interest rate for the full loan term.

No PMI. Private mortgage insurance is not included. PMI typically applies when down payment is under 20%.

Principal and interest only. Property tax and insurance (escrow) are calculated separately.

Retirement Calculators (401k, Roth IRA)

Constant return rate. Investment returns are assumed constant. Real returns vary year to year.

No sequence-of-returns risk. Results show average growth, not worst-case retirement scenarios.

No RMDs. Required minimum distributions are not modeled.

Update schedule

IRS tax brackets and retirement contribution limits get updated each fall when new figures are released — usually October or November for the following year. We update our calculators as soon as those numbers are published. State tax rates are reviewed every January. Each calculator page shows its last update date, so you always know how fresh the data is.

Limitations

These calculators are planning tools, not tax filing software. Results are estimates — useful for understanding your situation and making better decisions, but not a substitute for a licensed CPA, financial planner, or tax professional who knows your full picture.

If you have self-employment income, rental properties, significant investment income, or recently went through a major life event (marriage, divorce, inheritance), the simplified assumptions in our calculators may not capture your situation accurately. A professional is worth it for complex cases.

Questions about our methodology? Contact us →