Frequently asked questions
How the calculators work, what happens to your data, and where the maths stops.
Privacy and data
No. Every calculation runs in JavaScript in your browser. There is no account, no server-side calculator and no analytics on any calculator page, so your income, balances and rates are never transmitted anywhere. The only thing saved is a saved scenario or currency choice, and that lives in your own browser local storage - clearing site data removes it.
Yes, and there is no paid tier. There are no affiliate links, no sponsored rates and no upsells. The calculators are open to everyone.
No. There is no sign-in anywhere on the site. That is a direct consequence of the privacy model - if we do not want your figures, we do not want an identifier for you either.
Accuracy
The engine lives in lib/calculations.ts as pure, dependency-free functions, and every formula is documented in the source. It is pinned by a standalone test suite (npm run test:calc) that currently runs 290 assertions against hand-computed figures, including edge cases such as a 0% interest rate and term extensions.
No, and anyone claiming otherwise is overselling. Lenders can apply different day-count conventions, insurance and escrow assumptions, and rounding. Treat these numbers as a well-founded planning tool rather than a quote, and always confirm the final figures with your lender.
Because a lower monthly payment is not automatically a saving. If the new loan runs longer than the one it replaces, the old loan is paid off first and every remaining month of the new loan is money out with nothing to offset it. The popular shortcut of dividing closing costs by the monthly saving misses this entirely. Ours amortises both loans in full, so it reports the month the deal is permanently ahead, and tells you when a deal crosses back into the red.
Because a maximum sitting exactly on a debt-to-income ceiling is a number no lender will comfortably approve and no household should want. The maximum shows the edge of what the DTI limits allow; the recommended figure is the one there is room to plan against.
Using the calculators
Yes. The switcher in the header converts between eight currencies (USD, EUR, GBP, CAD, AUD, INR, JPY and PKR) and the choice persists in your browser. The underlying maths is done in the amount you type, so switching currency never silently re-converts a figure you already entered.
Yes, and the comparison matrix ranks on total lifetime cost rather than monthly payment, because a longer term always lowers the payment while raising the total. The site also deliberately does not repeat the common claim that avalanche is always the fastest payoff - it costs less interest, but the test suite contains a case where snowball finishes a month sooner while costing more.
Scenarios are saved to your own browser and can be reloaded, exported to CSV, or printed. Nothing is uploaded, so saved scenarios do not follow you to another device or browser.
The pages are static and lightweight, so once loaded they keep working on a weak or lost connection. The first visit needs a network request to fetch the page itself.
Getting help
Please tell us - include the figures you entered and what you expected instead. Bug reports are the easiest kind of message to act on, and the test suite exists precisely so a wrong figure can be pinned and prevented from coming back.
No. These are calculators, not advisers. They show you the arithmetic of a decision - what a payment is made of, what a refinance really costs, how long a debt takes to clear - but the judgement about which is right for you is yours, ideally with a qualified professional who knows your full situation.
Still stuck?
If your question is not here, ask it directly. Bug reports and awkward edge cases are the most welcome kind of message.