How We Check Our Math

Last updated: August 6, 2026

Every calculator on this site is built twice. The version you use is written first; then a second, independent implementation is written from the underlying formula or IRS instruction — deliberately not by copying the first — and the two are run against each other across dozens of scenarios, including the awkward ones: zero interest rates, income above the Social Security wage base, expenses larger than revenue, a 100% down payment. A calculator ships only when both implementations agree and every edge case behaves sensibly.

That process is not decoration. When we ran it in August 2026 it caught five real errors in our own tools before they reached anyone: a freelance rate formula that taxed deductible business expenses, a quarterly tax estimate that ignored the taxable-income ceiling on the qualified business income deduction, a 1099-versus-W-2 comparison that counted paid time off twice and failed to cap the employer Social Security contribution at the wage base, and a mortgage payment that omitted private mortgage insurance entirely. Each of those would have sent someone away with a materially wrong number.

Where the tax figures come from

The 2026 numbers used across the site — a $184,500 Social Security wage base, a $16,100 single and $32,200 joint standard deduction, and the seven federal income tax brackets — come from the Social Security Administration's annual announcement and IRS Revenue Procedure 2025-32. We check each figure against at least two independent publications before using it. Tax rules change every year; when the IRS publishes 2027 figures, these tools are updated and this page records the date.

What we deliberately do not do

We do not ask who you are, and nothing you type into a calculator ever leaves your browser — there is no server to send it to. We do not display user ratings or review counts, because we do not collect any and inventing them would be dishonest. And we do not claim professional credentials we do not hold: these tools produce careful estimates, not tax advice. For a filing decision, a return, or anything with real money at stake, talk to a qualified accountant.

Assumptions worth knowing

Some simplifications are unavoidable in a general-purpose tool. State income tax is estimated by applying your state's rate to profit after the self-employment tax adjustment, because every state defines its own deductions — that errs slightly high, which is the safer direction for a set-aside figure. Investment calculators compound monthly and ignore inflation, fees and taxes on gains unless stated. Mortgage results exclude closing costs. Where an assumption materially changes the answer, the calculator's own page says so.

Found a mistake?

Tell us. Corrections are the most useful message we can receive, and we would rather fix an error quickly than defend it. Write to contact@piggymath.com with the numbers you entered and what you expected — we reply to these first.