What Is A Mortgage Preapproval? Mortgage Preapproval is a document or letter from the lender stating how much they are willing to lend money to you to buy your home. Getting preapproval is the crucial step in buying a home. The preapproval is an indication that the lender is willing to move forward with the loan if the home meets the criteria expected or there is no drastic changes in your income or assets etc. The lender checks the borrower's creditworthiness based on income