There are many different ways to calculate a credit score. But you can reduce your chance of surprise if you have a good relationship with your bank or credit union. Going this route can help you get your score without paying for it.
Ask your banker if they can access your FICO score specifically for mortgages. You may also be able to request your score for free from a housing counselor that’s approved by HUD. There are a few variations that lenders can choose for mortgage applications, but it’s a far smaller pool than the dozens of methods you could see used otherwise. Doing this will give you a good idea of what you’re working with and whether you need to raise your score before applying.