During my tenure in the mortgage brokerage industry, one of the most recurrent causes for concern from borrowers, was how pulling one's FICO score affected credit.

The answer, like most things, isn't a simple yes or no, but a "depends."  The 3 credit bureaus: Equifax, Transunion, and Experian are secretive about the formula for determining the score. Just like Coca-Cola or Colonel Sanders, they don't want you to know the secret recipe. So, knowing exactly how each pull, and each type of pull will affect your credit is unknown.  Yet, there are certain, general aspects that we do know. 

Not all credit pulls are treated equally 

A credit card company is not averse to you shopping for the best rate on a loan. Thus if you have your credit pulled multiple times by several mortgage companies, you should not be dinged for it. Since, when your credit is pulled, the credit bureaus can differentiate between a credit card company and a mortgage company,  they treat each differently. If however, you have taken a trip to the mall and applied for 5 different credit cards at 5 different department stores, the credit bureaus make the assumption that you are looking to quickly in debt yourself, and in turn ding your credit for it. for this reason people make the assumption that all credit pulls will be detrimental to your credit

Time frame matters as well

As noted previously, a credit bureau can tell the difference between the different types of companies that are pulling your credit and will treat them differently. Even though, you are generally safe when having multiple mortgage brokers pull your credit, these pulls must be done within several weeks of eachother. If you are having your credit pulled by mortgage companies multiple times ever week, for 8 straight weeks, the assumption of the credit bureaus is no longer that you are shopping for the best rate, but that you simply getting denied over and over again for a mortgage. They also may assume that you are looking to purchase multiple homes at the same time. For both of these scenario's your credit will get dinged.

So when shopping for a mortgage, don't be afraid to have your credit pulled multiple times, just make sure you do it within a time frame of several weeks.