When you get a mortgage to purchase a home, the lender uses the lower of the agreed-upon purchase price or the property's appraised value to determine your maximum loan amount. The loan amount divided by the property home price equals your loan-to-value ratio, or LTV. That ratio is one of the major factors that lenders use to set your mortgage rate. If your LTV exceeds 80 percent, you'll probably be required to pay mortgage insurance, which increases your monthly payment. If the property appraises for less than the agreed-on purchase price, you are not usually required to complete the purchase.