How we verify the numbers

Every monthly payment shown anywhere on this site comes from a single equation, the standard fixed-rate amortisation formula:

M = P × [ r(1 + r)ⁿ ] / [ (1 + r)ⁿ − 1 ]

where P is the amount borrowed, r is the monthly interest rate (the annual rate divided by twelve) and n is the number of monthly payments. The schedule, the total interest and every threshold month mentioned in the guides are derived from that same function, run period by period.

This matters more than it sounds. A site with several calculators will eventually accumulate several copies of the same arithmetic, and the copies drift. When two pages of the same site disagree, there is no way for a reader to tell which one is right. Here, the calculators, the amortisation tables and the worked examples in the guides all call one implementation — so they cannot contradict each other.

Getting the formula right is the easy part. The realistic failure modes are an error in the implementation and a typo introduced when a number is copied into prose. So every figure that appears in a worked example is produced twice, by two independent calculations — the site's own code, and a second implementation written separately — and the two results are compared before publication. A figure that fails the comparison does not go on the page.

Where a number depends on a sequence rather than a formula — a complete amortisation schedule, a break-even curve, the month a balance crosses a threshold — both implementations run the whole sequence, not just the headline output. A correct monthly payment with a wrong schedule behind it is the kind of error a spot check will not catch.

• Interest rates in examples are illustrative. A rate printed today is wrong next month, so every example fixes a rate explicitly and shows what follows from it. We do not publish a “current average rate”, because we cannot guarantee one stays current.
• Tax, insurance and fees are inputs, not assumptions. Property tax rates, homeowners insurance, origination fees and mortgage insurance premiums vary by location, lender and borrower. You supply them, and the pages say plainly that you have.
• Rounding is disclosed. Monthly payments are shown to the cent and lifetime totals are rounded to the dollar. Where a displayed input is itself rounded — a half-payment of $948.10 standing in for $948.102… — the difference is small enough to move a lifetime total by a dollar or two, and the example stands on the exact value rather than the displayed one.

The output of these calculators is an estimate. It is not a loan offer, not a quote, and not financial advice. It cannot be: your lender applies its own fees, its own rounding conventions, its own day-count rules and its own escrow schedule, none of which a general calculator can know.

The documents that actually govern your loan are the ones your lender issues — the Loan Estimate, the Closing Disclosure and the promissory note. Where those differ from anything here, they win. See our disclaimer for the full statement.

Some rules genuinely differ by jurisdiction or by contract, and presenting one version as a national fact would be a defect, not a simplification. These include how a trade-in affects sales tax, the threshold and the procedure for cancelling mortgage insurance, income-driven repayment formulas, prepayment penalties, and the treatment of fees in APR.

On those points a page says so, describes the general shape of the rule, and points you at the document or the official guidance that settles it — rather than inventing a number that looks authoritative and is out of date.

If a figure on this site is wrong, we would rather hear it from you than not hear it at all. Email hello@loancalcly.com with the page and the number. A reported correction is re-run through both implementations before anything is changed, and the page's review date is updated when the content genuinely changes — not on every deployment.

Pages here carry the byline of David Chen, personal finance editor — one named person who is accountable for what is published, not a brand name standing in for nobody.

I write about borrowing costs and personal finance. I came to the subject from securities analysis, where the same amortisation mathematics decides what an instrument is worth: present value, discounting, and the month-by-month split between interest and principal.

I am not a lender, a broker or a mortgage adviser, and nothing on this site is personalised advice. What I bring to it is a habit carried over from quantitative work — never publish a number that has not been computed twice, by two independent routes.

The byline on every calculator and every guide links back to this page, and each of those pages carries the date it was last checked. What we will not do is attach a fabricated author, credential or testimonial to the site: a made-up expert is worse than no expert, and the whole point of this page is that the claims here can be checked.

Software is involved in producing this site — the calculators are software, and drafting tools are used to prepare the explanatory text. The standards above apply regardless of how a first draft was created: figures are recomputed independently, statements about rules are checked against primary documents, and a named editor reviews what is published.

LoanCalcly is free to use and funded by advertising and, where relevant, affiliate links. Advertising never influences a calculator's output — the arithmetic is the arithmetic. Sponsored or affiliate links are labelled where they appear, and our disclaimer explains how that works. We do not sell your information, because we do not collect it.