How we verify our calculators

Every number on this site is meant to be checkable, not just trusted. This page explains the process behind that claim: where the math comes from, how it is tested before it ships, how often the underlying data is reviewed, who is responsible for it, and what happens if something is wrong.

Editorial process

Every calculator starts from an authoritative primary source, not a guess. Depending on the topic, that source is IRS worksheets and publications, Consumer Financial Protection Bureau guidance, Department of Labor rules, TreasuryDirect documentation, the SEC’s Investor.gov, or the standard formulas used across the lending industry - whichever body actually governs the calculation. The source comes first; the calculator's logic is built to match it, not the other way around. Each tool's "How it works" section names the method it follows and links the primary source wherever one is published, so the math can be checked rather than taken on faith.

How the math is tested

Every calculator's engine is pure code, separate from the page that displays it, and is covered by an automated test suite (vitest) that checks its output against closed-form math and known edge cases before anything ships. If a change to an engine breaks a previously-verified result, the test suite fails and the change does not go live.

Annual data review

Figures that change every year - federal tax brackets, 401(k) contribution limits, state tax rates, and similar dollar amounts - live in a small set of dated data files, never hardcoded inside a calculator's logic. Each file is reviewed at least once a year against its primary source and updated for the new year as soon as the relevant agency publishes it. Year-specific numbers are always dated in the source file so it is clear which tax year or calendar year they apply to.

Who writes this

CentsMath is built and maintained by Tanish Sharma, an independent developer. I write every calculator, source every formula, and read every accuracy report personally. I am not a financial advisor, and nothing here is financial advice - see the About pagefor more on what these tools are and are not.

Correction policy

Found a number that looks wrong? Tell me - accuracy reports are prioritized ahead of everything else, because a calculator you cannot trust is worse than no calculator at all. Confirmed errors are fixed first, usually within days, and the underlying test suite is updated so the same mistake cannot silently return.