Whenever you decide to apply for a mortgage, the lender will verify not only one but all three credit scores from credit scoring bureaus, namely Experian, Equifax, and TransUnion. So once you decide to get a mortgage, always ensure that you have scores in all three services. If you have all three scores, the lender will pick the middle one. However, if you only have two, then the lower number will be taken into account. In case you have only one credit score, be ready that many lenders will not approve a mortgage for you due to the limited credit history.
Regarding the actual numbers, the lenders will have. Generally, if your credit score is high, such as 720 FICO points, then you get the best interest and so the best deal. If you have about 650-680 you still qualify for a mortgage but are put into a risk group, so your interest percentage will be much less attractive. Once your credit score drops below 620, be ready having problems with receiving a mortgage deal from any lender. FHFA and CFPB report that less than 7% of all lenders do give mortgages to people with such low scores.
Always remember that your particular lender might be using any other credit score calculating model within FICO or VantageScore frames. However, the numbers described above can give you a rough idea about your financial situation and chances for a great mortgage deal.