Interest rate versus APR: which number belongs in a loan calculator?
A contractual borrowing rate determines interest, while a broader annual cost measure may include fees. Using the wrong percentage can make a repayment estimate misleading.
Loan calculator →Read what each percentage measures
The borrowing rate prices the outstanding money. A broader measure such as APR can reflect specified fees and their timing as well as interest. Definitions differ by jurisdiction and product, so familiar initials do not guarantee identical treatment across countries. A repayment calculator needs a rate consistent with the selected interest convention, rather than whichever percentage looks most prominent in an advertisement.
See what one upfront fee changes
Imagine a one-year loan with 10,000 principal, 500 interest paid with the principal at year end and a 200 fee paid at the start. Net cash received is 9,800 and the final payment is 10,500. The cost over this single period is 700/9,800, approximately 7.14%, although the stated simple interest rate is 5%. This is an independently worked single-cash-flow illustration, not a universal formula for instalment-loan APR.
Enter fees according to how they are paid
Use the contractual borrowing rate for the monthly repayment model. A financed fee increases the amount borrowed; a separately paid fee belongs in a separate cost comparison. For instalments, irregular dates or several charges, consult the lender’s applicable disclosure rather than inserting the illustrative 7.14% above. This distinction lets the calculator estimate payments without claiming to reproduce every jurisdiction’s statutory APR calculation.
Try the calculators
- Loan calculator
Compare terms and see what borrowing will cost.
- Simple interest
Calculate interest without compounding.
- Return on investment calculator
Calculate net gain and ROI from cost, final value, income and expenses.