## Separate the three rate inputs
A market average is context, not a mortgage offer. UK Finance reported an average rate of 4.77% across new UK buy-to-let loans in Q4 2025. A live application still depends on the product rate, fees, stress rate, ICR and lender criteria available to that borrower and property.
The [PRA underwriting statement](https://www.bankofengland.co.uk/prudential-regulation/publication/2016/underwriting-standards-for-buy-to-let-mortgage-contracts-ss) covers ICR and interest-rate affordability stress testing for the firms in scope. It identifies the September 2016 statement as current and the January 2026 version as effective from 1 January 2027.
The Bank of England explains that [Bank Rate influences other interest rates](https://www.bankofengland.co.uk/monetary-policy/the-interest-rate-bank-rate). It is still not the quoted product rate or the lender stress rate. Save each as a separate field so a change in one does not silently overwrite the others.
## Read the lender criteria before modelling
The Mortgage Works publishes different ICRs for different application types. Its [current income criteria](https://www.themortgageworks.co.uk/intermediaries/lending-criteria/income) says the gross rent confirmed by the valuer must cover the mortgage interest payment by the applicable ICR. It also includes product fees added to the loan when calculating maximum borrowing.
Record the exact product, stress rate, ICR, LTV and fee treatment beside the model. Do not mix an average market rate with a different lender's ICR.
Create one comparison row per product. Include the fixed or variable period, reversion rate, product fee, early repayment charge, stress rate, ICR, maximum LTV, rent-supported loan and LTV-supported loan. Mark the evidence date so an expired product cannot remain the apparent winner.
## Calculate the two loan ceilings
The simplified rent-supported calculation is:
**Maximum loan = qualifying annual rent / (stress rate x ICR multiplier)**
Use GBP 18,000 qualifying annual rent, 5.5% stress and 145% ICR in the [buy-to-let stress and ICR calculator](/tools/buy-to-let-stress-icr-calculator). The rent-supported result is GBP 225,705.33 before LTV.
For a GBP 180,000 property at 75% LTV, the separate LTV ceiling is GBP 135,000. The lower ceiling is therefore GBP 135,000. At that loan, the required annual rent is GBP 10,766.25 under the controlled stress assumptions.
## Compare products on the same basis
For each product, preserve the quoted rate, stress rate, ICR, maximum LTV, product fee and expiry date of the evidence. Recalculate when any input changes.
Use the [gross and net yield calculator](/tools/gross-net-yield-calculator) for operating cash flow after the lender screen. The lender test uses qualifying rent; the yield model separately deducts management, maintenance, insurance and void assumptions.