A prequalification consists of a discussion between a home buyer and a loan officer. The loan officer collects basic information regarding the customer's income, monthly debts, credit history and assets, and then uses this information to calculate an estimated mortgage amount for the home buyer. The prequalification is not a full mortgage approval, but estimates what a home buyer can afford.
A preapproval, on the other hand, is a comprehensive approach using basic information as well as electronic credit reporting. Preapprovals, in most cases, are true mortgage commitments.
The lender commits to financing your home and indicates the total mortgage amount available to you.