Calculators / Methodology
Methodology
The formulas, assumptions, and lender benchmarks behind every calculator on this site. Each calculation is the same one UK commercial mortgage lenders use in underwriting.
Source of formulas
Every calculator on this site implements the standard finance formula for the metric in question. DSCR, ICR and debt yield use the canonical commercial real-estate finance definitions. The amortisation calculation in the repayment calculator uses the standard mortgage amortisation formula. None of the calculators attempt to be cleverer than the formula. They give the right number from the right inputs.
Lender benchmark thresholds are drawn from publicly disclosed product guides, broker panel commentary across the UK commercial mortgage market, and the experience of Commercial Mortgages Broker (CMB Finance Ltd) placing live deals across the active lender panel. They are working norms for May 2026, not a guarantee that any specific lender will hit them on any specific deal.
How interest is treated
Calculators on this site treat interest as the lender quotes it: annual percentage rate, applied monthly. Monthly interest is annual rate divided by 12. This is the standard convention for UK commercial mortgages and matches lender quotes.
The bridging calculator treats rates as monthly (because that is how UK bridging is quoted). It assumes serviced interest, not retained. On retained-interest bridges, the gross loan is larger than the net loan by the upfront interest deduction.
Per-calculator methodology
7 toolsDSCR Calculator
Whether the property or business generates enough cash to service the loan.
Benchmark. Lenders want 1.25x to 1.40x on owner-occupier, 1.40x to 1.60x on goodwill-heavy trading businesses.
Debt Yield Calculator
The belt-and-braces sanity check that protects against ICR being flattered by low rates.
Benchmark. UK commercial lenders want 8.5% to 10.5% on investment property.
ICR Calculator
The investment-property equivalent of DSCR. Tells you whether rental income clears interest with the cover lenders want.
Benchmark. Lenders want 140% to 175% depending on sector and LTV.
Repayment Calculator
Monthly payment, total interest cost and a year-one amortisation snapshot.
Benchmark. Owner-occupier deals typically run 15 to 25 years amortisation. Investment deals often go interest-only on 5-year fixes.
Stress Test Calculator
How your cover ratios degrade as rates rise. Lenders run this exercise before underwriting.
Benchmark. Lenders sanity-check that DSCR stays above 1.10x even at base + 2%.
Property Yield Calculator
The bedrock investment metric. Gross yield uses headline rent; net yield strips out running costs.
Benchmark. UK commercial yields range from 4.5% prime industrial to 8.5%+ secondary retail.
Bridging Cost Calculator
The real total cost of a UK commercial bridge, not just the headline monthly rate.
Benchmark. UK commercial bridging prices 0.70 to 0.95% per month plus 1.5 to 2.0% arrangement.
What the calculators do not do
- They do not price specific lenders. Calculators return the metric. Whether a particular lender will quote on the resulting deal depends on covenant, sector, geography, asset condition and dozens of factors a calculator cannot see.
- They do not model multi-tranche structures. Senior + mezzanine + JV-equity stacks are out of scope. The calculators assume a single senior facility.
- They do not include tax. Outputs are pre-tax. SDLT is included in the property yield calculator as an acquisition cost only.
- They do not advise. For illustrative purposes only. These calculators are educational. They are not advice. Actual lender pricing and underwriting decisions depend on covenant, LTV, sector, property condition and dozens of factors a calculator does not see. Always validate with a regulated advisor before committing to finance.
How the rate context fits in
Where current UK commercial mortgage rates sit week-by-week is published separately on the UK Commercial Mortgage Rate Tracker. Use the tracker to set realistic rate inputs on the calculators here. The rate tracker publishes ranges by category (owner-occupier, investment, semi-commercial, refinance, bridging) plus Bank of England Bank Rate and 5-year Gilt context.
Editorial independence
These calculators are educational. They are not paid placements for any lender or platform. Commercial Mortgages Broker (CMB Finance Ltd) does receive commission when placing live deals with lenders, but no calculator output on this site is influenced by that commercial relationship.