A mortgage agreement in principle (AIP) gives an estimate of how much a lender might lend and may show an indicative interest rate, but it is not a formal mortgage offer. The rate can change before you apply or receive an offer, particularly if the lender’s products or your circumstances change. AIPs often last around 30 to 90 days, and some involve a credit search, so check the lender’s terms first. For help comparing options, consider speaking to an FCA-authorised mortgage adviser.