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 by category (rents, goods, and services), applied to a national household budget baseline from the US Bureau of Labor Statistics Consumer Expenditure Survey.
• Retirement-income taxation — how each state taxes Social Security, pensions, and 401(k)/IRA withdrawals, curated from Kiplinger, AARP, and state Departments of Revenue for the current tax year and reviewed like any other datapoint.
• State-to-state migration — US Census Bureau, ACS State-to-State Migration Flows. We aggregate the published county-level inbound flows into a state-to-state matrix, then read each state's outflows off its transpose (the API leaves the direct out-migration field empty). "Net interstate migration" is total arrivals minus departures across the other 49 states; it excludes Washington, DC, US territories, and moves abroad.

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 deduction. Federal income tax assumes the standard deduction and excludes itemized deductions and credits; state income tax models each state's own deduction or exemption basis, described below.

State income tax modeling

Each state uses its own schedule — no income tax, a single flat rate, or graduated brackets — applied to a taxable base after that state's standard deduction or personal exemption. Where a state's deduction, exemption, or liability genuinely depends on income, we model that rather than pinning a single figure, so take-home is correct across the whole salary range:

• Phasing-out deductions and exemptions — states whose standard deduction or personal exemption shrinks as income rises (for example South Carolina, Wisconsin, and Connecticut) are modeled as a declining amount, not a fixed one.
• Massachusetts millionaire surtax — the flat 5% plus the 4% surtax on income over ~$1.08M is modeled as a 5% / 9% schedule.
• Alabama federal-tax deduction — Alabama lets you deduct the federal income tax you paid; we subtract the computed federal tax from the Alabama base.
• Utah taxpayer credit — Utah's flat rate is reduced by the taxpayer credit (a share of the federal standard deduction) that phases out with income.
• Maryland county income tax — Maryland's local income tax is layered on top of the state rate.

A few states require a documented approximation because part of their tax can't be captured by a state-level, no-dependents calculator:

• Maryland — the county local income tax varies from 2.25% to 3.20% depending on where you live. We apply a population-weighted statewide average of about 3.1%; your actual rate depends on your county.
• Connecticut — we do not model Connecticut's 3% benefit-recapture or high-earner tax-recapture add-backs, so the estimate is slightly low for incomes above roughly $56,000.
• Arkansas — we use the standard bracket schedule and standard deduction. Arkansas's separate low-income tax tables and a narrow bracket adjustment near $95,000 are out of scope, so the estimate is most accurate for typical middle incomes.
• Minnesota — the standard-deduction reduction for very high earners (AGI above ~$232,000) is not modeled.
• Utah — the taxpayer credit is modeled for filers with no dependents.

Every state page also shows its own as of date and a plain-language note describing its deduction basis and any approximation.

Cost of living

We take a national single-adult monthly budget by category and scale it to each state using BEA Regional Price Parities (US average = 100), then to your household size. Crucially, we use the category-specific parity for each line: housing follows the rents parity (which ranges from about 54 in West Virginia to 154 in California), food and transportation follow the goods parity, and healthcare and other spending follow the services parity. Using a category parity instead of a single all-items number is what keeps high-housing-cost states from being understated. Housing is also treated as largely shared, so it grows more slowly than the other categories 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.

How we check the tax numbers

Beyond our own unit tests, we cross-check every state's income tax against the open-source PolicyEngine US microsimulation model — an independent, academically-maintained implementation of federal and state tax law. For a single filer, our figures match PolicyEngine within about 3% in the large majority of states; the small remaining differences come from inflation-year timing on brackets or credits we note per state. Where a state's own rules can't be captured exactly, we say so on this page and in each state's data note.

Limitations

• Calculators are estimates for general information, not tax, legal, or financial advice.
• No dependents. Both federal and state income tax are modeled for a filer without children or other dependents. Households with kids often owe less thanks to child tax credits and dependent exemptions (which vary widely by state), so a family's real tax — especially head-of-household filers — can be lower than shown.
• We assume the standard deduction and exclude itemized deductions. State income tax models each state's own deduction, exemption, credit, and local-tax basis, with the documented per-state approximations described above.
• State-level figures — cost of living and Maryland's local income tax — use a single statewide value and do not capture within-state variation between counties or metros.

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