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Most of the calculators that rank for these terms are a single form. You enter a balance, a rate and a term, and you get a payment back. That answers a question next to the one most people arrive with, which is when the loan actually ends, what it will have cost by the time it does, and what changes if you pay more than you have to.

A schedule shows things a payment cannot. On $300,000 at 6.500% over thirty years the payment is $1,896.21, and of the first one, $1,625.00 is interest and $271.21 reaches the principal. The first payment that puts more toward the principal than toward the interest is number 233 of 360. After 180 payments — half the term, and $258,993.39 of interest — the balance is still $217,675.59, which is 72.6% of what was borrowed. Every one of those figures is a row in a table, and this site prints the table in full rather than summarizing it.

The arithmetic is written down as well as run. Methodology carries the formulas, the rounding rule — whole cents, interest rounded half-up once per period, the scheduled payment rounded up so a schedule can never run past the stated term — and a set of test vectors with their expected answers. A figure on this site is meant to be checkable, not taken on faith, and the $382,628.90 of total interest on that thirty-year example is the sum of a column rather than payment times term, which would read $6.70 higher.

The site is operated by ZW Studio LLC, a limited liability company formed in the State of New Jersey, United States. The contact address is support@zwstudiollc.com, which contact repeats along with a note on what is useful to send. ZW Studio LLC builds small single-purpose tools and this is one of them: there is no editorial staff behind it, no panel of reviewers, and no claim to either.

The site earns from display advertising and nothing else. There are no lender relationships, no offers, no rate tables, no affiliate links and no sponsored placements of any kind. Nobody pays for a mention here, because there is nothing to mention and nowhere to be sent.

That has one consequence worth stating plainly. Since no result leads anywhere that pays, the defaults in a form, the order of a schedule and the wording of an explanation are answerable only to whether they are right. Ads sit below the answer and never above it — the result panel is the first thing on a calculator page, and that ordering does not bend for an ad slot.

A calculator is a narrow instrument, and this one is kept narrow on purpose. Four things it will not grow into:

Nothing you type is transmitted. Every schedule is built in your browser from the numbers in the form, and no balance, rate, term or payment is sent anywhere, logged or retained. There are no accounts and no sign-in, and the only thing stored between visits is a record of your consent choice, kept in your own browser.

The one exception is deliberate and yours: the copy-link button writes your inputs into the address bar so you can bookmark a scenario or send it to someone, and that link carries numbers and nothing else. The advertising and measurement the site does run are requests the page itself makes, and privacy describes them, what they collect and how long it is kept. They are separate from the calculator, which stays in the browser either way.