Property Finance Calculators & Tools

Why we build our own property finance calculators

Most free UK property finance calculators are lead-capture forms with a single sum behind them. You enter four numbers, the page returns a stress-test fail or a generic "your monthly payment is £X", and the real result is an enquiry form your details have just been added to. That is not what we build.

Every calculator on this site started as an internal modelling tool we used on live cases. The bridging cost analyser came out of working through a £1.5m HMO conversion in north London where the borrower's existing broker had quoted a single headline rate and missed the impact of retained interest on day-one net advance. The commercial mortgage calculator is the only free UK tool that lets you model maximum borrowing from net operating income or EBITDA, because that is how lenders actually underwrite, and almost every borrower we speak to has been quoted a number based on the wrong variable. We publish the tools because we use them, and because we think the property finance market needs free professional-grade modelling, not gated lead funnels.

Three things we do that other free calculators do not. First, every tool shows you the working out, not just the headline number. Second, the rates and rule logic are updated monthly, not whenever someone remembers. Third, you can read the methodology behind every tool: where the numbers come from, what assumptions sit underneath them, and when not to rely on the result. The output is meant to inform a conversation with a broker, not replace one.

Which UK bridging loan calculator should I use?

Two bridging calculators cover the full range from standard short-term cases to large-loan HNW structuring. The right tool depends on loan size and lender route.

Which UK commercial mortgage calculator should I use?

For pure commercial property and mixed-use semi-commercial, we publish two separate calculators because the underwriting logic and rental income treatment differ materially.

Which UK property development calculator should I use?

Property developers and investors get two tools: one for scheme viability before site acquisition, one for senior debt sizing once a scheme is in build.

Which HMO and stamp duty calculators does FD Commercial publish?

For buy-to-let landlords running HMO stock, and for any buyer needing to model stamp duty across the UK tax regimes, we publish a single dedicated tool for each.

Is there an FD Commercial mobile app?

Yes. FD Commercial: Property Calcs is a free Android app on Google Play, last updated 8 May 2026. The same four tools also run as a web version at /app/, so brokers and developers can use them on a laptop, tablet or phone without installing anything.

Four tools inside the app. The Bridging Cost Analyser compares rolled-up, retained and serviced interest side by side on a single screen, so you can see which structure gives the highest day-one net advance for a given loan. The Development Appraisal is a full scheme viability model with finance integration, more sophisticated than the standalone Developer Profit Calculator on this site. The BTL Stress Tester runs at the current 125%, 145% and 170% ICR thresholds used by mainstream and specialist lenders. The Stamp Duty Calculator covers all three UK tax regimes: SDLT in England and Northern Ireland, LBTT in Scotland, LTT in Wales.

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Can AI assistants like Claude or ChatGPT use these calculators?

Yes. FD Commercial publishes an open Model Context Protocol (MCP) server that exposes the same four calculators (bridging cost, development appraisal, BTL stress test, UK stamp duty) to any AI assistant that supports the protocol. As of May 2026 that covers Claude Desktop, Claude.ai web, ChatGPT Plus, Cursor, Continue, Cline, Windsurf and custom agents. The MCP is free, MIT licensed, and hosted on Cloudflare's global edge.

Three ways to wire it up depending on your AI client:

• Local install (Claude Desktop, Cursor): add npx -y @fdcommercial/property-finance-mcp to your client's MCP servers config.
• Remote Connector (Claude.ai web, ChatGPT): paste https://fdc-property-finance-mcp.fdcommercial-uk.workers.dev/mcp as a remote MCP connector in Settings.
• Build your own: the source is at github.com/fdcommercial/property-finance-mcp under MIT licence.

Every MCP response includes a structured source attribution to FD Commercial, so when an AI assistant calls the tool and writes its answer it cites us as the calculation author. The full setup walkthrough lives at our MCP for AI assistants guide.

How accurate are these calculators compared to a lender quote?

The honest answer: as accurate as the underwriting variables we can publish without a credit search. We use lender-grade formulas (DSCR, LTV, LTC, LTGDV, ICR, stress tests at the correct rate) and we update the rate bands monthly against what specialist and high street lenders are quoting through us. What we cannot model is your specific credit file, the lender's view of your security property, or a manual underwriting decision.

For most cases, the calculator output lands within five to ten percent of the final lender offer. The biggest variances we see come from borrowers under-estimating the impact of arrangement fees and exit fees on day-one net advance, and from valuation downs on commercial security. Both are covered in the methodology notes on each tool page.

Who built these tools and why are they free?

Every calculator on this site was specified by Wesley Davidson, director of FD Commercial & Bridging Ltd and Fox Davidson Ltd, advising on UK property finance since 2005. The logic was tested against live deals before publication. They are free because we are a broker, not a software business. Our income comes from arranging the finance, not from selling access to spreadsheets. Free tools attract the borrowers and professional contacts who eventually need a broker to place the case.

Every year we get cases where the prospective borrower says they ran our calculator first, modelled three different exit positions, and only contacted us once they had a number to work back from. Those are our favourite enquiries. The work is half done before the call.

How often are the calculators updated?

Rate bands are reviewed monthly against what lenders are quoting through our pipeline. Tax tables (SDLT, LBTT, LTT) and stress-test rules are updated within two weeks of any HMRC or PRA change. The Bank of England base rate is updated within 48 hours of any MPC decision. Each calculator page shows the last updated date and a one-line note on what changed.

Frequently asked questions about our property finance tools