RenteRadar

RenteRadar.be is a free, browser-based tool built around a single, surprisingly hard question for Belgian homeowners: is it actually worth refinancing my mortgage right now? Instead of a vague gut feeling or a sales conversation at the bank, it gives a clear, numbers-backed answer in under a minute.

How it works

You enter the essentials of your loan — its start date, its type (fixed, or one of the common variable formulas), your interest rate, and optionally your outstanding principal. RenteRadar then plots your rate against the official Belgian market rate (NBB/ECB MIR) from the month you signed to today, and returns a plain-language verdict: how far your rate sits above or below the market, your estimated switching costs, the break-even threshold, and how many months it would take to earn those costs back within your remaining term. Because not everyone knows their loan details by heart, it also shows exactly where to find each number — on the loan deed, in your bank's app, on the annual tax certificate, or on the amortization schedule.

Privacy by design

Every calculation happens locally, in the browser. Nothing is stored, nothing is transmitted, and there's no account to create. Just as deliberately, RenteRadar isn't a credit intermediary: it gives no advice, submits no applications and takes no commission from banks. The verdict is a neutral starting point — the decision stays entirely with the user.

The challenge

The hard part is turning messy, hard-to-find inputs into an answer people can actually trust. That means modelling the real Belgian market rate over two decades (NBB/ECB data, with a composite series for the years before October 2006), supporting several loan types, and estimating switching costs and break-even honestly rather than optimistically. All of it has to land as one glanceable verdict and chart — and the entire computation has to run client-side, so sensitive financial details never leave the device. On top of that, the tool has to gently solve the "I don't know my own loan terms" problem that would otherwise stop people before they start.

My role

[Assuming this is your own project — correct me if the framing's off.] I designed and built RenteRadar end to end: the in-browser calculation engine, the market-rate model based on NBB and ECB data, the visualization and verdict UI, and the trilingual (NL/FR/EN) site.

Outcome

RenteRadar is a free, no-account web tool, available in Dutch, French and English, that turns a question normally reserved for bankers and brokers into something a homeowner can answer themselves — privately, in their browser, in well under a minute.