## Start with the underwriting inputs
The [PRA buy-to-let underwriting statement](https://www.bankofengland.co.uk/prudential-regulation/publication/2016/underwriting-standards-for-buy-to-let-mortgage-contracts-ss) includes expectations for ICR tests and interest-rate affordability stress tests for firms in scope. The [FCA mortgage conduct sourcebook](https://www.handbook.fca.org.uk/handbook/MCOB/) contains conduct rules and guidance for regulated mortgage and home-finance activities within its scope.
The Mortgage Works [current income criteria](https://www.themortgageworks.co.uk/intermediaries/lending-criteria/income) says gross rental income confirmed by the valuer must cover the monthly mortgage interest payment by the applicable ICR. Its page lists different ICRs for different applicant and property types and includes product fees added to the loan when calculating maximum borrowing.
## Use the rent-supported loan formula
The Bricks & Yield simplified equation is:
**Maximum loan = qualifying gross annual rent / (annual stress rate x ICR multiplier)**
The [buy-to-let stress and ICR calculator](/tools/buy-to-let-stress-icr-calculator) uses the qualifying gross rent entered by the user. It does not model lender rent haircuts, voids, product fees or lender-specific criteria.
## Complete the controlled calculation
Use these controlled inputs:
| Input | Value |
| --- | ---: |
| Qualifying gross annual rent | GBP 18,000 |
| Annual stress rate | 5.5% |
| ICR multiplier | 145% |
| Property value | GBP 180,000 |
| Controlled LTV input | 75% |
GBP 18,000 divided by 5.5% multiplied by 145% gives a rent-supported loan of GBP 225,705.33. GBP 180,000 multiplied by 75% gives a separate LTV ceiling of GBP 135,000. GBP 135,000 is lower, so the LTV ceiling binds in this controlled case.
Reverse the same calculation at GBP 135,000 debt. Stressed annual interest at 5.5% is GBP 7,425. Multiplying GBP 7,425 by 145% gives required annual rent of GBP 10,766.25. The controlled GBP 18,000 rent is above that amount.
## Read the output boundary
The calculator finds rent-supported debt before applying the separate LTV ceiling. When an LTV is supplied, it can divide the rent-supported loan by that LTV to show an implied price before SDLT and deposit-mix costs. The final property screen uses the lower evidenced ceiling for documented review only.
## Keep operating costs separate
The [gross and net yield calculator](/tools/gross-net-yield-calculator) separates annual gross rent from management, maintenance, insurance and void costs. It calculates net rent before borrowing and does not calculate lender stress, finance, tax or after-tax cash flow.
Store the operating-cost result separately from the lender stress result. The first is a property cash-flow screen; the second is a simplified lender debt screen.