Add-On Interest Calculator
Add-On Interest Calculator
The add-on interest method calculates interest on the full original principal for the entire loan term upfront, then adds that interest to the principal and divides the total into equal monthly payments. Because interest is charged on the original balance the whole time — even as you pay it down — this method produces a much higher effective rate than standard amortization at the same stated percentage.
Some consumer loans, retail installment plans, and older-style auto loans still use add-on interest, and understanding the difference matters: a "6% add-on" loan can have an effective APR closer to 11%, since standard amortization would let the falling balance reduce future interest.
- Interest Calculated Upfront: Total interest = Principal × Rate × Years, calculated on the full original amount for the whole term.
- Costs More Than It Looks: The effective interest rate on an add-on loan is roughly double the stated rate, since your balance is actually declining but you're still charged as if it weren't.
- Watch for This Method: Always ask whether a loan uses add-on interest or standard amortization — the same stated rate produces very different real costs.
Why does add-on interest cost so much more?
Because interest is calculated as if you owed the full original balance for the entire term, even though you're paying it down each month — you're effectively paying interest on money you've already repaid.
How do I know if my loan uses add-on interest?
Check your loan agreement or ask your lender directly — if the total interest was calculated once upfront on the full principal rather than recalculated monthly on a declining balance, it's an add-on loan.
Add-On Interest Calculator
The add-on interest method calculates interest on the full original principal for the entire loan term upfront, then adds that interest to the principal and divides the total into equal monthly payments. Because interest is charged on the original balance the whole time — even as you pay it down — this method produces a much higher effective rate than standard amortization at the same stated percentage.
Some consumer loans, retail installment plans, and older-style auto loans still use add-on interest, and understanding the difference matters: a "6% add-on" loan can have an effective APR closer to 11%, since standard amortization would let the falling balance reduce future interest.
- Interest Calculated Upfront: Total interest = Principal × Rate × Years, calculated on the full original amount for the whole term.
- Costs More Than It Looks: The effective interest rate on an add-on loan is roughly double the stated rate, since your balance is actually declining but you're still charged as if it weren't.
- Watch for This Method: Always ask whether a loan uses add-on interest or standard amortization — the same stated rate produces very different real costs.
Why does add-on interest cost so much more?
Because interest is calculated as if you owed the full original balance for the entire term, even though you're paying it down each month — you're effectively paying interest on money you've already repaid.
How do I know if my loan uses add-on interest?
Check your loan agreement or ask your lender directly — if the total interest was calculated once upfront on the full principal rather than recalculated monthly on a declining balance, it's an add-on loan.