Methodology

CostByState exists to answer money questions with numbers you can trust and verify. Every figure on the site is sourced, dated, and reproducible. This page documents where the data comes from, how each calculator works, and how often things update.

Data sources

We prefer official, free, primary sources. Each datapoint on the site shows its source and the date the source data describes (as of), not the date we fetched it.

• Federal income tax & FICA — IRS annual inflation adjustments (Revenue Procedure) and the Social Security Administration wage base. Entered once per tax year.
• State income tax — each state's revenue department, mirrored through the open-source PolicyEngine US parameter set and spot-checked against the state authority.
• Home prices — Zillow Research Home Value Index (ZHVI), state level.
• Household income & population — US Census Bureau, American Community Survey (ACS) 1-Year.
• Electricity prices — US Energy Information Administration (EIA), residential retail price.
• Mortgage rates — Freddie Mac Primary Mortgage Market Survey (PMMS).
• Regional cost of living — US Bureau of Economic Analysis (BEA) Regional Price Parities, applied to a national household budget baseline from the US Bureau of Labor Statistics Consumer Expenditure Survey.

How each calculator works

Paycheck calculator

Take-home pay is gross pay minus federal income tax, state income tax, and FICA (Social Security up to the annual wage base, plus Medicare with the additional high-earner surtax), after any pre-tax deductions. Traditional 401(k) contributions reduce income tax but not FICA; HSA contributions reduce both. Federal and state income taxes are computed on their own taxable-income bases using each schedule's brackets and standard deduction. We assume the standard deduction and do not model itemized deductions or credits.

Cost of living

We take a national single-adult monthly budget by category and scale it to each state using that state's Regional Price Parity (US average = 100), then to your household size. Housing is treated as largely shared, so it grows more slowly than food, transportation, or healthcare as household size increases. You can override any category with your real spending.

Salary needed

We estimate your monthly living costs for your household and lifestyle, then work backwards through the same tax engine — federal brackets, FICA, and state tax — to find the gross salary whose take-home covers those costs. It uses bisection over the forward paycheck calculation, so the "salary needed" number can never drift from what the paycheck calculator would show.

Verification and updates

Data is refreshed by an automated pipeline that opens a monthly pull request with a diff of every changed figure. A human reviews and approves each change before it reaches the site — no number is published without that review. The pipeline validates every value against a schema and flags any figure that moves more than 30% from the prior month. When a fetch fails, we keep the previous value rather than publish a bad one. Fields that a source only updates annually (such as tax brackets or ACS income) stay fixed between releases.

Limitations

• Calculators are estimates for general information, not tax, legal, or financial advice.
• They assume the standard deduction and exclude credits, local income taxes, and one-off costs.
• State-level cost figures use a single statewide price level and do not capture within-state variation between metros.

Questions about a specific number or source? Contact us — corrections are welcome and taken seriously.