Rules applied by a Lender to determine what is a sustainable level of Mortgage for a Borrower to support. With Residential Mortgages a Lender will rely almost solely on a client’s income and expenditure to make this calculation, and clients should expect to complete a Monthly Budget Plan. Lenders will take a proportion of the surplus income and then work backwards from there, probably at a Stressed Rate, to determine what Loan the Borrower can qualify for. For BTL, a Lender will take the rental received, deduct a percentage to allow for maintenance, voids and tax, and then look for the remaining rent to cover a higher Stress Rate.