Editorial & Engineering Methodology

How we build, source, verify, and update every calculator on CalculatorsAndMore.com.

Why we published this page

A calculator is only as good as the formula behind it and the process used to verify that formula. Most calculator sites do not tell you where their numbers come from. We do. If you are going to make a decision based on something this site produced, you should be able to audit it.

This page describes the process we follow for every calculator on the site, from the first research pass to the fixes we push after launch.

Our six-step process

1. Source the formula

Every new calculator starts with at least one authoritative source. For finance, that is usually an IRS publication, a federal agency (SSA, CFPB, HUD), or a widely cited textbook formula. For health, it is the CDC, WHO, NIH, or a peer-reviewed source (Mifflin-St Jeor, Harris-Benedict, WHtR, ACSM). For physics and chemistry, NIST or ISO. For math, a standard definition from a college-level reference. We do not invent formulas.

2. Implement the math in plain TypeScript

Calculator logic is handwritten in TypeScript, not generated. We keep math and UI separate so each formula can be read in isolation. Where regulations change year over year (tax brackets, FICA limits, contribution caps), the reference year is constant at the top of the file and shown on the page so you know exactly which year the math reflects.

3. Verify against a second source

Before a calculator ships, we cross-check its output against at least one established tool or published worked example (SmartAsset, Bankrate, calculator.net, or the reference source's own example). If our result disagrees by more than rounding error, the calculator does not ship until we understand why.

4. Document on the page

Every calculator page shows the formula it uses, a worked example with real numbers, and a plain-English explanation of each input. We also list common gotchas (compounding frequency, early-payment assumptions, unit conventions) so you can spot the case where a generic calculator does not fit your specific situation.

5. Update on a schedule

Calculators that depend on annual figures (tax brackets, Social Security, FHA limits, TSP contribution caps) are reviewed every January and updated within two weeks of new figures being released. Calculators based on stable formulas (BMI, loan amortization, temperature conversion) are reviewed annually for tooling and UI, not math.

6. Fast correction cycle

If you email us a bug report with a clear reproduction, we aim to push a fix within 72 hours. Math errors take priority over everything else on the roadmap. When a calculator is corrected, the page's last-updated date reflects the change.

Sources we rely on

These are the authoritative sources we default to when researching a calculator. We list them here so you know the pool our numbers come from:

  • Finance & taxes: IRS (irs.gov), Social Security Administration (ssa.gov), Consumer Financial Protection Bureau (cfpb.gov), HUD, Federal Reserve (FRED), and the IRS annual tax bracket releases.
  • Health & fitness: CDC, NIH, WHO, American College of Sports Medicine (ACSM), and the peer-reviewed papers that define the formulas we use (Mifflin-St Jeor 1990, Harris-Benedict revised, Jackson-Pollock body fat, Naegele's rule, and so on).
  • Units & physics: NIST (Special Publication 811), ISO/IEC, and the International System of Units (SI) brochure.
  • Construction: ACI 318 (concrete), ASHRAE, local IBC/IRC references, and manufacturer technical data sheets for material coverage.
  • Math: Standard college-level definitions (Rosen, Strang, Stewart) and numerical methods references.

What we deliberately do not do

  • We do not use AI to generate calculator math. Large language models are great at prose and terrible at reliably citing tax rates, benefit formulas, and regulation-bound numbers. Every formula is researched and written by hand.
  • We do not store your inputs. All math runs in your browser. There is no server that sees your loan balance, weight, salary, or medical inputs.
  • We do not gate accuracy behind payment. Every calculator and every feature is free. There is no "premium" version with different math.
  • We do not manufacture numbers. If a formula has a contested definition (think body fat, ideal weight, risk scores) we document the exact version we implemented and why.

How we handle edge cases

Every calculator has boundary conditions that trip up generic implementations: leap years, daylight saving time, negative balances, integer-only inputs, currencies with non-decimal cents, imperial versus metric defaults, and so on. When we find one that matters, we document the decision on the calculator page rather than hiding it.

For example, the loan calculator uses monthly compounding with a fixed end-of-period payment convention, which matches how US mortgages are actually serviced. If you are comparing to a tool that uses a different convention, you will see a small difference. We explain this on the page so the gap is never a mystery.

Reporting an error

If you think a calculator is wrong, we want to hear about it. Email hello@calculatorsandmore.com with the calculator name, the inputs you used, the result you got, and the result you expected (with a source if you have one). Math errors jump to the top of the queue.

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