Pre-qualification is an informal discussion between borrower and lender. The lender estimates the amount that you can borrow based solely on what you tell them about your income and assets. The lender does no verification and is not bound to make the loan when you're ready to buy.  

To a seller, a lender's pre-approval letter is considerably stronger than a pre-qualification letter. Loan pre-approval is based on documented and verified information regarding your employment, your income, your liabilities, your assets and the cash you have available to close on a home purchase. If a seller knows your financing is secure, your offer is stronger. Pre-approval also gives you peace of mind as you shop for a home, knowing that you will qualify for the proper mortgage amount.