It is wise to keep your options open and recieve as many pre-approvals as possible. As Mr. Koren explains, the lock in program is out there if you want it. However, the rates do changes, and if you feel you are getting a good rate by all means lock it in. I perfer to ask my buyers to search as long as possible because the interest rate and other specifics to a loan can change after you have found a home and can vary depending on the type of home you buy. A pre-approval allows you to put in an offer on a property and get your offer accepted faster than a buyer with no pre-approval. The pre-approval will give you more bargining power when the offer is presented to a seller. Good luck in your home search.