Mortgage lenders apply a formula to the amount you can borrow which is based on a multiple of the income(s) of the borrower(s). The aim is to make sure that you are not over stretched and can afford to keep up with repayments.
Typically lenders will lend a sum equivalent to 2 or sometimes 3 times the main income plus second income, or 2.5 times the joint income.
Less commonly other much higher multipliers are used such as 4 or more times the main income.
These are known as High Multiplier Mortgages and are normally for people with reliably growing income, or where partners income is present but being ignored (e.g. because of a bad credit history, lack of accounts etc, but where you know that you can rely on it).
They are normally only given on a case by case basis.
