What Actually Determines a Loan's Total Cost
A loan's total cost is set by three factors working together: the principal (how much you borrow), the interest rate (the annual cost of borrowing, as a percentage), and the term (how many months you take to repay it) — of the three, term has the largest effect on total interest paid, since a longer term multiplies the number of months interest accrues on the remaining balance.
The same loan amount can cost dramatically different total amounts depending on how these three factors are combined — understanding the relationship helps you evaluate an offer rather than just comparing monthly payments.
Principal and rate set the baseline
The principal is the starting point — interest is calculated as a percentage of whatever balance remains, so a larger principal means more dollars of interest at any given rate. The interest rate then sets how quickly that cost accrues; even a 1-2 percentage point difference compounds meaningfully over a multi-year term.
Term is the multiplier most people underweight
Extending a loan's term lowers the monthly payment, which feels like savings — but it also means more months of interest accruing on a balance that shrinks more slowly. Two loans with an identical rate and principal can differ by thousands of dollars in total interest purely because of term length.