what credit score do banks really need to purchase a house?

As noted by others 620 is a good rule of thumb. However, you should not assume that you will not be able to buy if your score is a little lower. If you have questions, you should talk to a mortgage broker for four reasons. 1) Your interest rate will depend to some extent on your credit score, but also other financial information you provide; 2) your credit score is NOT written in stone. A good broker can help you improve your score with some simple adjustment or by finding mistakes in the credit report and correcting them; 3) a broker can and will look at other financial information from you that will affect your ability to borrow. It is not just your credit score that matters. 4) brokers can search for the best loan product for you in particular You may have noticed that I mention "brokers," but not necessarily banks. Some banks (and other financial institutions) can also help you. However, some banks may have limited or no options if you don't qualify for their in-house products. And some loan officers at banks seem a little less motivated to work with you if you cannot qualify immediately. Best, Ron Rovtar, Prudential Real Estate of the Rockies, Boulder CO

Most lending institutions require a minimum 620 credit score, however, consulting a mortgage officer is the best first step in the home buying process. There are many other factors including income, expenses, flood insurance, etc. that they can go over with you. Once you are pre approved you can search with an agent and feel confident in the price range that best fits your needs.

Most banks require a minimum middle credit score of 620 for a conventional or FHA mortgage. There are some that go lower, but there are other rules that apply for that type of a loan.