About Mortgage Calculator

Who builds this

Mortgage Calculator is built and maintained by TBS Digital, an independent studio in Bordeaux, France. Contact for corrections or feedback.

How the math is checked

The core engine is the standard amortization formula M = P × [r(1+r)ⁿ] / [(1+r)ⁿ − 1], the same one Excel's PMT() function uses. Outputs are reconciled to the cent against Excel's PMT, IPMT and PPMT on a fixed-rate loan with no extras.

Country-specific layers are sourced from official documentation and reviewed when rules change:

United States — PMI: cancellation thresholds (80% LTV borrower request, 78% automatic) follow the Homeowners Protection Act of 1998 and the CFPB guidance. Average rates referenced from the Freddie Mac PMMS.
United Kingdom — Stamp Duty: brackets and surcharges per HMRC SDLT, including the 3% additional-property surcharge and first-time buyer relief.
France — Frais de notaire and assurance emprunteur: rates from service-public.fr (logement ancien ~7-8%, neuf ~2-3%) and the Code de la consommation articles on the TAEG calculation.

If you spot a discrepancy with current rules in your country, tell us — corrections are pushed the same week.

Why we built this calculator

Honestly? Frustration. Every "free mortgage calculator" we tried while modelling our own deals did at least one of these things: hid the amortization schedule behind an email signup, pretended PMI didn't exist, only worked for one country, or rounded so aggressively that the totals didn't actually add up. None of them showed the full month-by-month breakdown without trying to extract a lead.

So we built ours. The full schedule is on the page, no signup, no email gate. PMI auto-applies and auto-removes per the Homeowners Protection Act. Three countries (US, UK, France) are first-class citizens — not afterthoughts bolted on with a currency dropdown. The math closes to zero in the final payment, the way a real loan does.

How we keep it accurate

We test the calculator's output against trusted reference implementations: Excel's built-in PMT() and IPMT() functions, the Federal Reserve's published mortgage worksheets, and the official simulators published by major French and UK retail banks (Crédit Agricole, BNP Paribas, Halifax, Nationwide). On a fixed-rate loan with no extras, our output matches those references to the cent.

The country-specific layers — UK stamp duty brackets, French frais de notaire, US PMI removal logic — are sourced from official government documentation (HMRC, the French government's service-public.fr, the CFPB) and reviewed periodically as rules change. If you spot a discrepancy with current regulations, please tell us and we'll fix it.

What this calculator doesn't do (yet)

We're not going to pretend the tool is complete. Honest list of things on the roadmap:

Adjustable-rate mortgages (ARMs). The current engine assumes fixed rates only. ARM modeling — with index-plus-margin reset logic — is planned for v2.
Bi-weekly payment schedules. Currently you can model the equivalent via extra principal payments, but we'd like a dedicated bi-weekly toggle.
Refinance comparison. Right now you can run two scenarios side by side manually. A real refi calculator with break-even analysis is coming.
More countries. Canada and Germany are next on the list, in that order.

Open and free, supported by ads

The calculator is and will remain free. There's no premium tier, no "unlock the export feature" upsell, no email collection. The site is supported by Google AdSense — that's it. We don't collect personal data, we don't sell to lenders, we don't run affiliate links. See the Privacy Policy for the full picture.

Get in touch

Bug reports, feature requests, accuracy corrections, or just a hello — drop us a message. The site is small enough that you'll get a reply from a real person, usually within a day or two.

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