Editorial Methodology

How we build, source, and review every calculator on ScoutMyTool.

ScoutMyTool ships free, transparent calculators and document tools. This page describes how we build them, what we cite, when we review them, and what we deliberately don’t do — so you can decide how much to trust each result.

1. How a calculator is built

Every calculator starts from a primary source — the IRS revenue procedure for tax brackets, the BLS CPI series for inflation, NIST SP 811 for SI unit conversions, ISO 8601 for date math, the SSA wage-base announcement for FICA, peer-reviewed clinical formulas for health calculators, and so on. We avoid building calculators where there is no authoritative source.

The formula is implemented in plain TypeScript and committed to source control. We test against canonical worked examples before shipping. For finance and tax tools, we verify against IRS Publication 17 / state instructions where applicable.

2. What you see on every tool page

  • Primary result — the headline number, with the units and rounding that the source authority uses (not arbitrary precision).
  • Breakdown — the intermediate steps so the math is reproducible by hand.
  • Step-by-step working — the exact arithmetic shown so you can teach someone else or check our work.
  • Authority citation — a link to the source document (IRS, BLS, NIST, ACOG, ISO, etc.) so you can verify the inputs we used.
  • Limitations / disclaimer — what the calculator does not model. We try to be specific (e.g. state tax tools say "uses top marginal rate; actual liability typically lower due to state brackets and deductions").
  • Frequently asked questions — schema-marked so search engines can surface them as featured snippets.

3. Sources we trust

By cluster, the authorities we lean on for primary data:

  • Tax & income — IRS Revenue Procedures, IRS Publications, SSA cost-of-living announcements, state revenue departments.
  • Finance & investment — SEC Investor.gov, CFPB rulemakings, Federal Reserve FRED for time-series, Trustees Reports for Social Security projections.
  • Health — CDC growth charts (for BMI under-20s), WHO BMI ranges, ACOG for pregnancy timing, NIH formulas (BMR Mifflin-St Jeor, Harris-Benedict), peer-reviewed clinical literature for body-fat and lab-value calculators.
  • Construction & trades — NEC for electrical sizing, IRC for residential framing, ASHRAE for HVAC, ACI for concrete mix design.
  • Math & science — NIST DLMF for special functions, ISO 8601 / IETF RFC 3339 for date math, BIPM SI brochure for units.
  • Cooking — USDA FoodData Central for nutrition, King Arthur Baking and Modernist Cuisine baker’s percentages, sous-vide times from Douglas Baldwin.

4. Review schedule

Each calculator has a Last reviewed date shown in the footer of its page. Time-bound calculators (federal tax brackets, state rates, FICA wage base, IRS contribution limits) are reviewed and updated whenever the relevant authority publishes new figures — typically within 30 days of the release. Year-stable calculators (geometry, statistics, unit conversion) are reviewed annually unless a user reports an issue.

If you find a calculation you believe is wrong, please contact us with your inputs and expected result — we read every report and either fix or document the discrepancy within a few days.

Independent formula verification (July 2026)

On 2026-07-07 we ran a formal cross-verification audit against the ten most-viewed calculators on ScoutMyTool. Each tool’s compute() function was extracted from the source, independently re-implemented from the primary authoritative reference, and run against multiple known-good test cases. All ten passed to the cent:

  • Mortgage & Loan Calculators: verified against the standard amortization formula and cross-checked against bankrate.com and CFPB Regulation Z amortization spec on 6 test cases including zero-rate and extreme-rate edges.
  • BMI Calculator: verified against WHO Technical Report Series 894 on 5 test cases (metric + imperial). Uses exact NIST conversion factors (0.45359237 kg/lb, 2.54 cm/inch).
  • Age Calculator: verified across 7 tricky calendar cases including leap-year Feb 29 births, year-boundary transitions, and same-day cases. UTC-safe arithmetic with round-trip validation to prevent Feb 30 silent overflow.
  • Compound Interest: verified against Excel’s FV()formula on 6 test cases across five compounding frequencies (annual, monthly, continuous, and mixed principal+contribution scenarios).
  • Income Tax Calculator: 2026 brackets verified against IRS Rev. Proc. 2025-32 Section 4.01 Tables 1–4. Standard deductions match IRS publication. Progressive bracket math verified via manual bracket-by-bracket calculation on 5 income scenarios.
  • BMR / Calorie Calculator: all three formula options (Mifflin-St Jeor 1990, Harris-Benedict revised Roza-Shizgal 1984, Katch-McArdle) verified against original published equations.
  • Home Affordability Calculator: verified against CFPB 28/36 rule on 3 income + debt scenarios.
  • Percentage Calculator, Retirement Calculator: verified against standard textbook formulas.

Zero calculation bugs were found in the ten tools audited. The re-verification script and test cases are archived and can be re-run whenever the underlying tool code changes. If you want a copy of the test spec for a specific tool, ask via the contact form.

5. What we don’t do

  • We don’t auto-generate calculator content with AI. Every formula, worked example, FAQ answer, and limitation note is written by a human. We use AI as a spell-checker and grammar assistant, never as the primary content author.
  • We don’t fabricate sources. Every citation links to a real document from a real authority. If we can’t find an authoritative source for a calculation, we don’t ship that tool.
  • We don’t give legal, tax, medical, or financial advice. Our calculators are decision-support tools, not professional advice. For consequential decisions, consult a licensed professional.
  • We don’t store or upload your input data. Calculators run entirely in your browser; nothing you type is sent to our servers. (PDF and image tools that process files run client-side too, with a small number of exceptions clearly noted on the tool page.)
  • We don’t add affiliate links inside calculations. If we recommend a paid product, it’s called out explicitly as a recommendation, not woven into the output.

6. About the operator

ScoutMyTool is built and maintained by the ScoutMyTool editorial team, an independent developer. The site is not venture-funded, not a Wirecutter-style affiliate review hub, and not part of a larger publisher network. The codebase is hand-written TypeScript / Next.js. The motivation is simple: there are tens of thousands of free calculators on the web; most are ad-stuffed, mobile-hostile, and unmaintained. We try to do better on all three.

7. Corrections and feedback

The fastest way to report an error is via the contact form. We read everything. Corrections that change a calculation result are deployed within 48 hours and the calculator’s Last reviewed date is bumped.

Last reviewed: . Page maintainer: the ScoutMyTool editorial team, Founder. Questions:admin@scoutmytool.com.