Last updated: October 23, 2026. This page explains how PayPlot creates, checks and updates its calculators and guides.
Our standards
- Primary sources first. Data comes from official statistics, standards bodies or the original publisher, and each page names its source and the period covered.
- Show the working. Each calculator states its formula and assumptions, with a worked example you can verify.
- Test before publishing. Our automated tests cover payment formulas against published examples, amortization schedules that sum to the loan amount, PMI cancellation timing, extra-payment savings and CSV output. A failing test blocks publication.
- Independence. Advertisers and affiliate partners have no say in what we publish or how a result is calculated.
Methodology
Payments use the standard amortization formula M = P·r(1+r)^n / ((1+r)^n − 1) with monthly compounding. Savings growth compounds monthly with deposits at month end. Results are before taxes and fees, and example rates on pages are illustrations, not offers or quotes.
Sources we use
- Standard amortization and compound-interest formulas
- U.S. Census Bureau, American Community Survey 2020–2024 5-year estimates, tables B25103 and B25077 (property tax by ZIP and state)
- NAIC / Insurance Information Institute, average homeowners (HO-3) premium
- Freddie Mac, guidance on private mortgage insurance cost; Homeowners Protection Act of 1998 (PMI cancellation at 78% LTV)
How content is written
Pages are researched and edited by Alex. We use software, including AI writing tools, to help draft explanations and to generate pages from structured data (for example, one page per country or per loan amount). Every figure comes from the calculator engine or a cited data set, not from a language model, and generated text is reviewed against the source before publication. Pages that would add little beyond an existing page are excluded from search indexing.
Updates and corrections
We refresh data when the publisher releases a new edition and record the date on each page. If you spot an error, please contact us; confirmed errors are corrected promptly and the page date is updated.
Limits
Calculators give estimates for general information. They are not personalised advice; see our terms of use.