Our Methodology
How our calculators work, where our data comes from, and how we keep everything accurate.
Our Principles
Every PropertyCalcHub calculator is built on three principles: accuracy, transparency and simplicity. We use official government and regulatory data sources, explain the formulas we use, and design our tools so anyone can understand the results — not just financial professionals.
Data Sources
| Data Type | Source | Update Frequency |
|---|---|---|
| UK SDLT rates & thresholds | HMRC — GOV.UK | On each Budget/change |
| Scotland LBTT rates | Revenue Scotland | On each change |
| Wales LTT rates | Welsh Revenue Authority | On each change |
| UK mortgage rules | FCA Mortgage Market Review | Annually |
| Canada stress test | OSFI B-20 Guideline | On each change |
| CMHC insurance premiums | CMHC | On each change |
| US lending rules | CFPB / Fannie Mae | Annually |
| Australian lending | APRA prudential standards | Annually |
| UK rental benchmarks | ONS, Zoopla Rental Market Report | Quarterly |
| UK house prices | ONS House Price Index | Monthly |
Calculator Formulas
Stamp Duty (SDLT)
We use the standard progressive band calculation: each portion of the property price falling within a band is taxed at that band's rate. For example, a £300,000 property in England: £0 on the first £125,000 (0%), £2,500 on £125,001–£250,000 (2%), £2,500 on £250,001–£300,000 (5%) = £5,000 total. First-time buyer relief, BTL surcharges and non-resident surcharges are applied on top.
Mortgage Repayment (Amortisation)
Monthly payments use the standard amortisation formula:
Where P = principal loan amount, r = monthly interest rate (annual rate ÷ 12), n = total number of monthly payments. Interest-only payments = P × r.
Rental Yield
Gross yield = (Annual rent ÷ Property value) × 100
Net yield = ((Annual rent − All annual costs) ÷ Property value) × 100
Annual costs include agent fees (% of effective rent), maintenance, insurance and void period losses.
Cap Rate
Cap rate = (Net Operating Income ÷ Property value) × 100
NOI = Effective Gross Income (gross rent less vacancy) minus all operating expenses (management, maintenance, insurance, property taxes). Mortgage payments are excluded from NOI — cap rate is an unlevered metric.
UK Affordability (Income Multiple)
Based on standard UK lender criteria: conservative 4× income, standard 4.5×, maximum 5× gross annual income. We apply a stress test at pay rate + 3% to check affordability under the FCA's prescribed testing methodology. Joint applications use combined income.
Canadian Stress Test (OSFI B-20)
Qualifying rate = max(contract rate + 2%, 5.25%). We apply this to income multiple calculations to show the true maximum borrowing under OSFI rules.
Section 24 Tax Impact
Pre-Section 24: landlord deducts full mortgage interest from rental income before calculating tax. Post-Section 24 (current UK law): landlord pays tax on full rental profit (after non-finance costs), then receives a 20% tax credit on mortgage interest. The difference shows the additional tax burden for higher-rate taxpayers.
Update Schedule
We update our calculators promptly when tax rates, thresholds or lending rules change. Our last comprehensive update was May 2026, incorporating the April 2025 SDLT threshold reversion and October 2024 BTL surcharge increase to 5%.
Spotted an error or outdated figure? Email us: [email protected]