How calculators are built

Each calculator starts with a user problem: estimating a payment, comparing options, converting units, or planning a cost. We then define the inputs, formula, assumptions, result breakdown and page explanation.

Formula transparency

Where possible, pages include the calculation formula in plain language. For example, mortgage tools separate principal and interest from tax, insurance, PMI and HOA so users understand what drives the monthly payment.

Estimate-based tools

Some calculators depend on tax rules, local rates, lender terms, payment processor fees, property rules or health assumptions. These calculators are labeled as estimates and should be used for planning, not final professional advice.

Quality checklist

• The page has a clear purpose and useful inputs.
• The result gives a practical breakdown, not just one number.
• Important assumptions are visible.
• The page includes related calculators for the next user task.
• Weak or duplicate calculators are removed from the public index.