How Our Bridging Loan Calculator Works

Where do the rate bands come from?

Every rate band in the calculator is set against live UK lender pricing that FD Commercial sees through its own broker pipeline. We arrange bridging facilities from £250,000 to £15m across the full lender panel, from clearing banks down to specialist short-term lenders. What lenders are quoting through us in any given month is what the bands reflect.

We do not publish individual lender rates by name in the calculator. Lender pricing changes weekly, sometimes daily on specific products, and a rate offered to one borrower at 60 percent LTV on a clean owner-occupier residential security will not necessarily be available to a different borrower on commercial security at the same LTV. Naming a lender at a fixed rate would mislead more borrowers than it would help. Instead, the bands we publish represent the realistic range across the active lender panel for a given combination of LTV, security type, and borrower profile.

Three external data points anchor the bands. The Bank of England base rate, currently 3.75 percent as of April 2026, feeds the underlying cost of funds across the market. The Bridging and Development Lenders Association (BDLA) publishes quarterly lending volumes and average loan size, which we cross-check against our own pipeline data. Where rates move materially in either direction (typical lender repricing happens 8 to 12 times per year across the panel), the calculator bands are updated within two weeks. Bank of England base rate moves trigger a 48-hour update.

What we have seen over the last 18 months is that calculator rate bands published by other UK brokers and lenders frequently lag the market by 3 to 6 months. Most are static figures someone set when the page launched and nobody updated since. If you are using a free UK bridging calculator that was last updated more than a quarter ago, the headline rate is almost certainly wrong.

How does the calculator compute the cost of rolled-up, retained and serviced interest?

The three interest structures behave very differently mathematically, and the calculator shows all three side by side because the choice of structure can move total cost by 5 to 15 percent on the same gross loan. Here is exactly how each one is computed.

Rolled-up interest

Rolled-up interest is calculated monthly and added to the loan balance at the end of each month. Next month's interest is then calculated on the new (higher) balance. This is compound interest applied monthly.

Formula: Balance(n) = Balance(n-1) × (1 + monthly_rate), applied month by month for the full term. Total interest cost = final balance minus original gross loan. Total amount to repay at exit = final balance plus exit fee (if applicable).

Worked example. £500,000 gross loan, 0.85 percent per month rolled-up, 12-month term. Month 1: £500,000 × 1.0085 = £504,250. Month 2: £504,250 × 1.0085 = £508,536. Month 12: £553,231. Total interest cost = £53,231. Total to repay at exit = £553,231 plus any exit fee. The calculator shows both the running balance month by month and the final repay figure.

Retained interest

Retained interest is calculated for the full term upfront, then deducted from the day-one net advance to the borrower. The borrower receives less cash on day one but the loan balance is fixed for the full term and no monthly interest is paid. Lenders prefer retained interest on cases where the borrower has no monthly income to service the debt and the exit is a clean sale or refinance at term end.

Formula: Retained interest = Gross loan × monthly_rate × term_months. Day-one net advance = Gross loan minus retained interest, minus arrangement fee, minus legal, minus valuation, minus any other lender deductions. Total cost = retained interest plus all fees.

Worked example. £500,000 gross loan, 0.85 percent per month retained, 12-month term. Retained interest = £500,000 × 0.0085 × 12 = £51,000. Day-one net advance before other fees = £449,000. The borrower receives £449,000 in cash (minus arrangement, legal and valuation) and the loan repays at £500,000 at term end. Total cost = £51,000 plus fees. Notice that on a 12-month term the rolled-up structure costs slightly more (£53,231) than the retained structure (£51,000) because rolled-up compounds. On shorter terms the gap narrows; on longer terms it widens.

Serviced interest

Serviced interest is calculated monthly on the original loan balance and paid by the borrower each month. The loan balance does not grow. At exit, the borrower repays the original gross loan plus any exit fee.

Formula: Monthly payment = Gross loan × monthly_rate. Total interest cost over term = Monthly payment × term_months. The borrower's cash flow during the term needs to support these payments.

Worked example. £500,000 gross loan, 0.85 percent per month serviced, 12-month term. Monthly payment = £500,000 × 0.0085 = £4,250. Total interest cost = £4,250 × 12 = £51,000. The borrower pays £4,250 every month for 12 months and repays £500,000 at exit. Total cost identical to retained on a 12-month term, but cash flow profile completely different: borrower needs £4,250 a month spare to keep the loan in good standing.

One observation from live cases. About a third of the cases we look at where the borrower has self-selected serviced interest could have been done on rolled-up at a similar total cost with much less cash flow strain during the term. Borrowers often pick serviced because it "feels" cheaper. It is not always cheaper. The calculator showing all three side by side is intended to flatten that bias.

What is day-one net advance and how does the calculator compute it?

Day-one net advance is the single most under-understood figure in UK bridging finance. It is the cash actually transferred to the borrower (or to the borrower's solicitor's client account) on the day the loan completes. It is almost never the same as the gross loan amount.

Day-one net advance formula: Gross loan − arrangement fee − retained interest (if applicable) − broker fee (where charged) − legal fees deducted from advance − valuation fee − any other lender deductions.

Worked example. £500,000 gross loan, retained interest structure at 0.85 percent per month for 12 months, 2 percent arrangement fee, broker fee paid separately (not deducted from advance), £1,500 legal deduction, £950 valuation. Day-one net advance = £500,000 − £51,000 (retained interest) − £10,000 (2% arrangement) − £1,500 (legal) − £950 (valuation) = £436,550. The borrower's solicitor receives £436,550 in cash on completion. This is the number that matters for whether the borrower can actually do the deal they intended to do.

The calculator displays day-one net advance prominently because borrowers consistently under-estimate the gap between gross loan and net advance. In retained-interest structures it is often 10 to 15 percent below the headline gross loan figure. On a 24-month retained bridge at 0.85 percent the gap widens further. The calculator makes the number unavoidable.

How does the calculator handle loan-to-value (LTV)?

LTV is computed as gross loan divided by lender-assessed property value, expressed as a percentage. The calculator takes both inputs (loan amount and property value) and returns the LTV. The output then determines which rate band applies.

LTV bands typically used by the calculator (these are realistic UK market bands as of 2026 and may move with the market):

• Up to 50% LTV: Cheapest pricing tier. Most lenders quote bottom-of-range rates here. Suitable for asset-rich borrowers using bridging as a strategic structuring tool rather than to maximise leverage.
• 50% to 65% LTV: Standard pricing tier. The middle of the market for residential security. Lender appetite is widest here, choice is greatest.
• 65% to 75% LTV: Higher pricing tier. Fewer lenders compete, rates lift 0.10 to 0.20 per month over the standard tier. Most common LTV band for owner-occupier residential bridges.
• 75% LTV+: Top of the market for residential bridging. Pricing lifts further, lender choice narrows materially. Above 80% LTV typically requires cross-collateralisation against a second security or HNW private bank routing.

Important: the calculator's LTV calculation is based on the value you input, not the value the lender's RICS surveyor will eventually report. Valuation downs are common on commercial security (10 to 20 percent below borrower expectation is normal), less common on standard residential. If you suspect a valuation risk, model the calculator at 90 percent of your expected value to stress-test the LTV impact.

What does the calculator not model?

Three categories of variable are deliberately not modelled, because no calculator can model them honestly without a credit search and case-by-case underwriting:

Your credit profile. Adverse credit, recent missed payments, IVAs, bankruptcies, CCJs and DMPs all materially affect lender appetite and pricing. The calculator output assumes a clean profile. Borrowers with adverse should expect tighter pricing, lower LTV ceilings, and a narrower lender shortlist.

The lender's view of the security. Two factors matter most. First, the desktop or full RICS valuation can come in 5 to 20 percent below borrower expectation, especially on commercial property, unusual residential security (short lease, listed, restricted use), or rural assets. Second, lender appetite for the property type varies enormously. Some lenders will not touch agricultural, others have no appetite for HMOs above 6 beds, others avoid London ground-floor commercial. The calculator does not screen for this.

Manual underwriting decisions. Complex income (carried interest, deferred bonus, RSU vesting, profit share, foreign income), unusual ownership structures (offshore, trust, multiple SPVs), and non-standard residency all push the case into manual underwriting. The outcome depends on the underwriter, the lender's risk appetite that month, and how well the case is packaged. No calculator can predict it.

When should you not rely on the calculator output?

Three situations where the calculator output, on its own, is not enough:

Loans above £1m. Above £1m the lender routing changes. Private banks, family offices and specialist HNW lenders enter the panel, and their pricing models look nothing like the standard specialist bridging market. We publish a separate HNW Bridging Loan Calculator that handles three-route comparison, cross-collateralisation and extended-term HNW structuring. Use that one above £1m.

Cases where lender appetite is the binding constraint, not pricing. Uninhabitable property, short lease (under 70 years), restricted-use commercial, agricultural with farming income, listed buildings with category restrictions, or any property where the lender panel narrows to two or three willing parties. In these cases the question is not "what rate" but "which lender will touch it at all". Talk to us first.

Adverse credit, complex income, non-standard residency. Where the underwriting decision is manual, the calculator output is indicative at best. Use it to model "what good looks like" and then talk to a broker who can match the case to the right manual underwriter.

How often is the calculator updated?

Rate bands are reviewed monthly against live lender pricing observed through the FD Commercial broker pipeline. Bank of England base rate decisions trigger an update within 48 hours. Stress-test rule changes (PRA, FCA) trigger an update within two weeks. Tax-related changes that affect the broader bridging market (SDLT thresholds, surcharge changes) are reviewed within two weeks of publication.

The calculator page itself shows the last-updated date in the page footer. If you are using the calculator and the rate seems materially different from a quote you have received, check the date and, if it is more than 30 days old, contact us for a current rate band check.

How accurate is the calculator compared to a real lender quote?

For most cases the calculator output lands within 5 to 10 percent of the final lender offer. The biggest variances we see in live cases come from three places. Arrangement fees and exit fees on day-one net advance are routinely under-estimated by borrowers, especially the impact of a 2 percent arrangement on a £500k+ loan. Valuation downs on commercial security can pull the LTV up enough to push the loan into a higher pricing tier. And manual underwriting outcomes on complex profiles are inherently unpredictable.

For internal credit committee screening (institutional investors, family offices, professional landlord portfolios) the calculator output is a reasonable indicative figure used as a first-pass screening tool. Several of our institutional clients run new opportunities through the calculator before bringing the case to us for formal terms. Treat the output the same way: a strong first-pass number, not a binding quote.

Can AI assistants call this calculator directly?

Yes. The same formulas behind the web calculator are exposed as an open Model Context Protocol (MCP) server, so AI assistants like Claude, ChatGPT and Cursor can call them and get back the same numbers you would see on this site. The hosted endpoint runs on Cloudflare's global edge network and is free to use.

Four tools are available through MCP: bridging_cost_analyser (this calculator), development_appraisal, btl_stress_tester and uk_stamp_duty_calculator. Every response includes a structured source field attributing FD Commercial, so AI clients reading the response will cite the calculation back to us in their answer.

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

• Claude Desktop or Cursor (local install): add npx -y @fdcommercial/property-finance-mcp to the MCP servers block of your client config. The package is published openly on npm.
• Claude.ai web or ChatGPT Connectors: paste https://fdc-property-finance-mcp.fdcommercial-uk.workers.dev/mcp as a remote MCP connector in client settings.
• Build your own AI agent: the source code is at github.com/fdcommercial/property-finance-mcp under MIT license. Fork it, embed it, or call the hosted endpoint as a JSON-RPC 2.0 service.

This is the first UK property finance broker MCP we are aware of. It exists because we believe AI assistants will increasingly be the first port of call for borrowers researching bridging finance, and we would rather the answers they give be grounded in the same calculations we run on live cases than in approximations.

Frequently asked questions about the methodology