When it comes to getting a mortgage, this is the most common way lenders work out how much you can borrow. The standard multipliers are three times a single person's salary, or two-and-a-half times a couple's joint salary. So if you were earning £20,000 a year, you could borrow £60,000 (20,000 X 3). Add your partner's salary of £20,000 and the amount you can borrow increases to £100,000 (40,000 X 2.5).