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CALCBLOC / METHODOLOGY

Methodology

Last verified:

This page explains exactly where CalcBloc's numbers come from, how we check them, and how we keep them current. If you find something that does not match an official source, please tell us.

1. Official sources only

Every tax figure on CalcBloc comes from the government body that sets it:

  • Federal income tax withholding: IRS Publication 15-T, Federal Income Tax Withholding Methods, for the tax year, and the current Form W-4.
  • Social Security, Medicare and supplemental (bonus) withholding: IRS Publication 15 (Circular E), Employer's Tax Guide.
  • Brackets, standard deduction and other inflation-adjusted amounts: the IRS revenue procedure published for the year (for 2026, Rev. Proc. 2025-32), plus the IRS's guidance on new laws.
  • State income tax and withholding: each state's department of revenue or taxation, using its employer withholding guide, formulas or tables for the year.
  • State payroll taxes: the state labor or employment agency that runs the program.
  • Local income taxes: the city, county or state agency that publishes the rate.
  • Labor rules such as overtime: the U.S. Department of Labor.

Third-party sites (other calculators, payroll companies, tax blogs, encyclopedias) may help us find a document or cross-check a result, but they are never the source of a number. Our own memory is not a source either: we fetch the document. If an agency's site blocks automated downloads, we try the document's direct link, the agency's other pages or the state's legislative site, and we record what we did.

2. Every record carries its source

Tax data lives in structured data files, one federal file and one file per state for each tax year. Every record in those files stores four things alongside the numbers:

  • sourceUrl: the link to the official document;
  • sourceTitle: the exact document name, such as "Publication 15-T (2026), Worksheet 1A";
  • retrievedAt: the date we fetched it;
  • notes: anything a reader or reviewer should know, such as the page or table used, or how we interpreted an ambiguous rule.

Calculator pages and state pages list these sources. Figures that appear in our articles but are not part of the tax engine, such as a state's sales tax rate, are kept in a separate facts file with the same four fields, and they are shown with a link to their source.

Our articles never contain hand-typed tax figures. Every rate or dollar amount in the text is pulled from the data files or calculated live, so when the data is corrected, every page that mentions it updates.

3. Automatic validation

Every data file is checked against a strict schema before the site can be built. The command npm run data:validate confirms, among other things, that:

  • every required field is present and has the right type;
  • rates are decimals between 0 and 1, and brackets start at zero and rise in order;
  • every record has a valid source link, title and retrieval date;
  • each state's withholding parameters match the shape that state's formula expects;
  • states marked as verified also have their explanatory page content in place.

If any check fails, the build fails, and the site is not updated.

4. Tested formulas

The calculations are written as small, separate functions, one for federal withholding, one for Social Security and Medicare, one for bonus withholding, one for the federal return and one for each state's withholding method. Each is tested automatically:

  • Against the agencies' own worked examples. Where the IRS or a state publishes an example calculation, we reproduce it exactly as a test and cite the page.
  • Against hand-calculated cases. Before a state can be marked verified, it needs at least ten test cases across different salaries, filing statuses and pay frequencies, including pre-tax deductions and local taxes where they apply. The expected answers are worked out by hand, step by step, following the official method, and written into the test so anyone can check the arithmetic. They are never produced by running the code being tested.

The full test suite runs before every build. A failing test blocks the release.

5. Withholding vs what you owe

Most of our calculators show withholding: what an employer takes out of each paycheck using the official employer method for the year. That is not always the same as the tax you owe, which is figured on your return.

  • The paycheck calculator, bonus tax calculator and state comparison show withholding.
  • The federal income tax calculator shows your estimated tax for the year, the way Form 1040 figures it, and compares it with what you have had withheld.
  • State pages show both: the state's withholding method and its tax brackets for the return.

Each calculator's "How it's calculated" section lists its assumptions and what it does not model.

6. Verified and under review

A state's data is marked verified only when every number in its file comes from an official source fetched for that tax year and all of its tests pass. Until then it is marked unverified, and:

  • its pages show a "data under review" notice;
  • those pages are hidden from search engines and left out of our sitemap;
  • tables that list every state label it as under review.

We would rather show a gap than a guess.

7. Keeping data current

  • Staleness check. The command npm run data:stale lists every record whose retrieval date is more than 90 days old, so we re-check it against the agency's current version.
  • Annual refresh. Each year, when the IRS publishes the next year's inflation-adjustment revenue procedure and the new Publication 15-T, and as states publish their withholding guides, we add a new set of data files for the new year. Earlier years' files are kept rather than overwritten.
  • Mid-year changes. When a law or an agency changes a rule during the year, we update the affected records, their retrieval dates and notes, and re-run the tests.

Every calculator page shows the date its figures were last verified.

8. Reporting an error

If you think a figure is wrong, contact us with the page address and, if you can, a link to the official source that shows the correct figure. We check every report against the source. When we confirm an error, we fix the data, add or update a test so it cannot come back, and update the page's verification date. How corrections are handled is set out in our editorial policy.