Our Methodology

Formula Selection

Each calculator begins with a published formula, accepted mathematical relationship, or documented rule. The formula and variables are shown on the page.

Testing

The checklist covers known-value examples, zero and boundary inputs, unit consistency, rounding, and comparison with a primary or textbook source where available.

Content and Updates

Calculator-specific facts, assumptions, limitations, and sources matter more than word count. Tax, marketplace-fee, and regulatory tools require review when their rules change.