How we calculate & review

Last reviewed October 2026 · Written & fact-checked by the NumberBench editorial team

NumberBench tools are built to give clear, honest estimates and to show their work. This page explains where our numbers come from, how often we update them, and what they can and can't tell you.

Our approach

Every calculator runs entirely in your browser — your inputs are never sent to us or stored. Each tool shows the formula it uses in its “How it's calculated” section, along with a worked example, common mistakes, and the assumptions behind the result. Our goal is that you can see exactly how a number was produced and decide whether it fits your situation.

Data sources

State income tax	2026 single-filer and married-filing-jointly brackets and standard deductions from the Tax Foundation, “2026 State Individual Income Tax Rates & Brackets.” Excludes local income taxes, credits, and itemized deductions.
Property & sales tax	Statewide average effective property tax rates and statewide base sales tax rates (2025). Local rates vary by county/city and are entered by you.
Health tools	BMI uses the standard weight/height² formula; body fat uses the U.S. Navy circumference method; calorie/TDEE uses the Mifflin–St Jeor equation with standard activity multipliers.
Finance tools	Loan, mortgage, and amortization figures use standard time-value-of-money formulas. FICA uses the published Social Security (6.2%) and Medicare (1.45%) rates.
Manufacturing tools	Cost, DFA, OEE, takt/cycle-time, and scrap calculators use widely accepted industrial-engineering formulas, documented on each page.

The three kinds of benchmark

Not every comparison carries the same weight, so each benchmarked calculator labels what kind of reference it is showing:

Public data — official figures from government or market datasets (BLS, Census, IRS, CDC, Freddie Mac, the Federal Reserve, EPA). These are the strongest references, and where a public source exists we link it directly on the calculator so you can verify it.
Industry norm — measured sector averages and reference ranges (profit margins by industry, average APRs, restaurant food-cost ranges, marketplace fees).
Rule of thumb — widely used planning guidelines (the 28/36 housing rule, the 4% safe-withdrawal rate, world-class operations targets). Useful for orientation, not guarantees.

How often we update

Seven market-rate observations have a daily automated refresh attempt. They keep the source observation date, reject malformed or stale responses, and publish only after calculation checks pass. Other datasets follow their stated release cadence. An observation year, source release date, and page review date are different; older survey data is labeled with its actual period. Formula-based tools change when their methods or assumptions change.

Limitations

Our calculators are estimates for general information and education — not financial, legal, tax, medical, or professional advice. Tax results assume a single income and standard deduction, and exclude local taxes, credits, and special situations. For decisions that matter, confirm the figures with a qualified professional or the relevant authority (for example, your state Department of Revenue).

How pages are curated

A separate page should answer a distinct question or provide meaningfully different data. A different salary amount, test score, or age usually belongs as a selectable input in one maintained tool. State laws and tax-year tables can justify separate references because their rules differ. When pages overlap, their information is consolidated and old URLs redirect to the relevant calculator with the original input selected.

Our October 2026 review examined the structure of the full top-level inventory and the shared templates behind generated families. That structural review is separate from an expert review of every formula.

Expert review

Formula checks and source links help you inspect a result; they do not constitute independent professional approval. No unnamed outside reviewer should be assumed. A credentialed reviewer is identified only after reviewing the specific tool. Higher-stakes tools awaiting that review remain excluded from search indexing.

Corrections

Found a number that looks off? We want to know. Contact us with the calculator and the inputs you used, and we'll review it promptly.