Methodology and sources

One engine, one source of truth

Every figure on the site — the online calculator as well as the pre-computed salary pages — is produced by the same calculation engine (paie-engine) fed by a versioned parameter file (data/params/us/2026.json). Each parameter carries its official source, verification date and reviewer name; an audit blocks publication if any of these fields is missing or a check is older than twelve months.

Before publication, the engine is cross-checked against the official calculators of the market — IRS (Internal Revenue Service) and state revenue departments — on a truth table of cases, with a tight tolerance.

The verification pipeline

1. Read on the official source. Every rate is read directly on the reference publication — IRS Revenue Procedure 2025-32 for federal brackets and standard deductions, IRS Publication 15 and the SSA cost-of-living announcement for FICA rates and the wage base, and state revenue departments for state tables (FTB for California, the New York Tax Department, the EDD for SDI…) . Never a third-party site, never an unflagged year-over-year extrapolation.
2. Traced parameter. The value is written into the parameter file with its source URL, verification date and reviewer name — the table below is generated straight from that file.
3. Tested engine. The engine applies the parameters against the independent truth table; any drift beyond tolerance blocks publication.
4. Cent-level audit. At every site build, an audit replays each salary amount page through the engine and compares the HTML to the cent; a divergence fails the deployment.

When rates change

US payroll parameters move on an annual cycle: the IRS releases the indexed federal brackets each fall (Revenue Procedure), the SSA announces the Social Security wage base with the cost-of-living adjustment, and states publish their own tables on their own calendar. Where an official 2026 value was not yet published at verification time, the value in force is kept and flagged in the parameter notes — the flag is removed when the official table lands. The date shown at the top of this page is the most recent verification across all parameters.

Calculation scope

• Employee in the private sector, federal + state income tax, FICA (Social Security and Medicare, including the Additional Medicare withholding above its statutory thresholds).
• States parameterized: the ten shown in the calculator selector — including no-income-tax states (TX, FL, WA) and state payroll taxes (California SDI, WA Cares). Other states are not published yet rather than published approximate.
• Out of scope: pre-tax deductions that vary by employer (401(k), health insurance premiums), local income taxes (New York City…), refundable credits (EITC, Child Tax Credit) and itemized deductions.
• Results are indicative estimates — never a payslip, never legal or tax advice.

Official sources (2026)

The parameter file for this market is still being verified — every line will be published here with its official source and verification date when the engine goes live. A market is never published on approximate rates.

The full parameter detail (values, units, verification notes) is public in the project's data repository.