How this site earns trust

Methodology

Four rules govern every calculator on StubMath. They are constraints we accept, not marketing claims — and each one is checkable from this page.

1. The formula is on the page

Every tool shows its arithmetic in a worked trace — the same numbers the calculator produces, derived step by step. If you can't follow the math, we consider the page broken.

2. The test suite is public

The site currently ships 36 test cases with 96 assertions, listed in full at /methodology/test-cases/. The build refuses to publish if any assertion fails. The first case of every tool is that page's default display — what you see before touching an input is itself a tested value.

3. Only self-verifiable math ships

Our admission rule: a tool ships only if its correctness can be proven by unit tests alone, with no dependence on external jurisdiction datasets. A pay-raise percentage was right in 1987 and will be right in 2046. That's why you'll find no state tax withholding calculator here — those numbers change yearly across 50 jurisdictions and deserve a compliance function, not a hobbyist's promise. The single exception is one federal constant (the IRS 22% flat supplemental rate), always labelled as a preview and cited to Pub 15.

4. Primary sources or silence

Where a rule of law matters — overtime thresholds, rounding practices, severance requirements — we cite the regulation itself (29 CFR, IRS publications, DOL pages), and where we don't compute something, we say so on the page instead of guessing.

The tools

Review cadence

Every page carries a “Last reviewed” date. The IRS publishes next year's withholding materials in mid-December; the annual review happens inside that window, and any change lands in the changelog.