Interest is the lender's charge for letting the borrower use money over time.
Interest is the cost a borrower pays for using the lender’s money over time.
Interest strongly affects affordability. Two mortgages with the same starting balance can have very different monthly costs and total repayment amounts if their interest charges differ.
It also shapes how quickly the loan balance falls. Early in many mortgages, a larger share of the payment goes to interest and a smaller share goes to principal. Later, that balance shifts.
Interest shows up when shoppers compare offers, when the lender quotes a rate, when disclosures estimate borrowing cost, and every month after closing when the payment is applied.
Borrowers also encounter interest during refinancing decisions. Even a modest rate change can affect the payment, the long-term cost of the loan, and how quickly equity grows.
Two buyers borrow the same amount for the same length of time. The borrower with the higher interest rate usually pays more each month and much more over the life of the loan, even though the starting principal was identical.
Interest is not Principal. Principal is the debt itself. Interest is the price of carrying that debt.
Interest is also different from the overall Monthly Payment. The payment can include principal and interest, and it may also include taxes, insurance, or escrow collections depending on the loan setup.