To determine what you can borrow, lenders look at your ability to pay and typically allow between 30 and 40% of your net monthly income after tax to pay for all worldwide debts (including the new Spanish mortgage). If you have loans, mortgages or credit cards, these will be taken into account in the calculation, as well as rental payments, alimony (compulsory maintenance payments to ex-spouses/partners or in respect of any children from these relationships) and private school fees.