Methodology

This page explains how our calculators are built and how we keep their results reliable. We believe a tool is only as trustworthy as the method behind it, so we make that method visible.

Where the formulas come from

Each calculator implements the standard formula used in textbooks, professional software, or the relevant standards body for its field — for example, amortization formulas for loans, compound-interest formulas for savings, and published agency rules for tax and benefit estimates. The formula for each tool is shown on its page so you can verify it yourself.

How results are computed

All calculations run entirely in your browser using double-precision floating-point math. Nothing is sent to a server, which keeps your inputs private and makes results instant. Because computation is local, the same inputs always produce the same output, and you can check any result by hand.

How we test

Before a tool is published we run representative cases and compare the output against an independent reference. We test edge cases — zero, very large, and very small inputs — and clamp unrealistic values to prevent misleading results. Bugs found after launch are fixed and re-verified.

Regional and time-sensitive data

Some tools depend on data that changes — currencies, tax brackets, statutory rates, and contribution limits. We source these from official publications, label the year they apply to, and review them on a recurring schedule. Estimates are clearly marked as estimates, not official determinations.

Limitations

Our calculators are designed for general estimation and education. They cannot capture every rule, exception, or individual circumstance. For decisions that affect your health, finances, or legal standing, treat our output as a starting point and confirm with a qualified professional.