What Is an Interest Rate vs APR Comparison?

An interest rate versus APR comparison puts two loan offers side by side and shows which one is genuinely cheaper. The interest rate tells you what the principal costs; the APR tells you what the whole loan costs once lender fees and charges are folded in. Lenders can quote similar rates while charging very different fees, so comparing rates alone can lead you to the more expensive deal. This calculator computes both figures for both offers and reports the APR spread and the difference in total dollars paid.

The classic case it resolves is a lower rate with higher fees against a slightly higher rate with lower fees. Only after each offer's costs are expressed as an annual rate does it become clear which one actually leaves more money in your pocket over the life of the loan.

How It Works

For each offer the calculator computes the scheduled payment from the amortisation formula PMT = P x r / (1 - (1 + r)^-n) using that offer's rate and the shared term. It then adds the lender fees you enter to any prepaid per-diem interest based on that offer's own rate, and subtracts the total from the loan amount to find the net proceeds. The APR is the rate at which the present value of the payment stream equals those net proceeds, solved by bisection and annualised by multiplying by twelve.

With an APR for each offer the comparison is direct: the lower APR is the cheaper loan. The calculator also totals the cost of each offer as payments plus fees, so you can see whether the APR advantage translates into a meaningful cash difference. Because both offers share the same principal and term, every difference in the output is attributable to the rate and fee mix rather than to loan size or duration.

Understanding Your Results

The primary card names the cheaper offer by APR and reports the spread in points along with the total-cost gap. The three statistics underneath give each offer's APR and the cash difference between them. The breakdown table lines up interest rate, fees, monthly payment, APR and total cost for both offers, so you can see exactly where the advantage comes from, whether it is a rate edge, a fee edge, or both.

Summary Statistics collects the winner, the APR spread, the payments and fees for each offer, and the total cost of each. A few tenths of a point of APR can be worth thousands of dollars on a large, long-term loan, which is why APR belongs in any mortgage or auto-loan comparison. Note that some third-party fees may be excluded from a lender's own APR figure depending on loan type, so use the same fee set for both offers and treat the output as a comparison tool rather than a substitute for each lender's Loan Estimate.