Our Methodology — Formulas, Sources & Review Process
1. What every calculator must publish
Before any Reckonly calculator goes live, it must have four things on the page — in this order:
Written out completely, every variable defined. Not described in prose — the actual formula, in a code block.
Real numbers, every step shown. Before publishing, those exact inputs are entered into the live calculator and the output is confirmed to match. This is a release gate — not optional.
Bulleted and concrete. Not "results may vary" — exact statements like "fixed rate assumed for full term" or "PMI drops at 80% LTV based on original value."
What the calculator does not model, stated plainly. "Does not model variable rates" — not "may not cover all situations."
2. How we source rate data
For rate-sensitive tools — income tax, APR definitions — data is sourced in strict order of preference:
Never used as a source: SEO blogs, competitor calculators, AI-generated content, or any unverified secondary source — regardless of how authoritative they appear.
3. Review schedule
Every tool has a review cadence. Reviews are logged in the Changelog — including “reviewed, no change needed” entries. A published review trail is itself a trust signal.
4. Stale data policy
If a tax tool's rates cannot be verified for the new year, it continues showing the prior year's rates with a visible banner. If rates can't be verified at all, the page says so clearly and shows no figure. A tool that can't be maintained comes offline — a stale finance calculator is worse than no calculator.
5. How the code is built
Every calculator runs entirely in your browser using vanilla JavaScript — no framework, no external dependencies, no build step. The core calculation function in each tool is pure: no DOM access, no side effects. This makes it independently testable against a spreadsheet before any UI is involved.
Each tool passes a full pre-publish checklist covering: mathematical correctness on at least three scenarios, all edge cases (zero, empty, negative, very large values), date boundaries for the Age Calculator, output formatting, keyboard accessibility, screen reader announcements, mobile layout at 320px, and Core Web Vitals targets.
6. Privacy and analytics
Calculation inputs never reach any server. Analytics events fire for general signals — “calculator completed” — but never include the values you entered. Our privacy claim and our analytics code say the same thing. See the Privacy Policy.
See also: Sources · Disclaimer · Changelog
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