Which of the following can affect a borrower's interest rate?

The borrower's credit score is a key factor that significantly affects the interest rate offered on a mortgage. Lenders use the credit score to assess the borrower’s creditworthiness, which indicates the likelihood of the borrower repaying the loan. A higher credit score generally suggests a lower risk for the lender, often resulting in more favorable interest rates for the borrower. Conversely, a lower credit score is associated with higher risk, which typically leads to a higher interest rate to mitigate that risk.

While neighborhood crime rates can influence the overall desirability of a property and possibly its value, they do not directly affect the lender's decision on interest rates. The borrower's age is not a determining factor in interest rate eligibility, as lending laws prohibit discrimination based on age. Similarly, while the type of insurance (like homeowners insurance) is an essential component of the overall loan process, it does not directly impact the calculation of the interest rate for the mortgage itself. Therefore, among the options provided, the borrower's credit score is the most relevant and influential factor affecting the interest rate.