Pre-Qualified is only a guide.
Being Pre-Qualified for a mortgage means that a mortgage professional has taken a peek at what you earn, what you owe, and calculated a standard approach to affordability to arrive at an amount that tells you - how big a mortgage, or how many dollars you should be able to get from a Lender. Pre-Qualified is only a guideline
Pre-Approved gives you a comfort zone.
A mortgage Pre-Approval mean that a lender has verified income, outstanding credit balances, and has looked at a credit report in about the same detail as if you has already applied for the mortgage loan.
With a Pre-Approval Mortgage, you know where you stand as a borrower. You have a clear picture of the type of mortgage, the interest rate and what your mortgage payments will be. Plus, most lenders will give you a rate-lock for 60 or 90 days after the Pre-Approval Date, so you're not caught if market rates change while you're home hunting.
When you buy and submit the mortgage application, the Lender will re-verify assets, income and debt to ensure nothing has changed, since the Pre-Approval. The property will be appraised to ensure it meets Lender and Lending Ratio Guidelines. And It's important to note that even when you're pre-approved, the property must also be approved by the Lender, before you can get a "Mortgage Commitment."