When you’re ready to start viewing properties, it’s a good idea to get a mortgage agreement in principle from one or more lenders. This will give you a good idea of how much you can borrow. Estate agents may also want to see this to ensure you’re serious about buying. Before going ahead with an agreement in principle application, check whether the lender will carry out a credit check. This will usually appear on your credit file. An agreement in principle is generally valid for between 30 and 90 days and is an estimate rather than a guaranteed mortgage offer.