The dealer's monthly payment hides 21% in interest. Here's the math.

How much does a $75,000 truck actually cost when you finance it?

A used 2022 Kenworth T680 priced at $75,000. You put $10,000 down and finance $65,000 at 9% APR for 60 months. The dealer tells you the monthly payment is $1,349 and moves on to discussing the truck.

Here's what they don't tell you. Over 60 payments of $1,349, you pay a total of $80,940 to retire the loan. You borrowed $65,000. The difference, $15,940, is total interest paid. Add your $10,000 down payment and the total cash you spent to own that truck is $90,940. The truck cost $75,000 on the sticker. It cost you $90,940 to acquire. That's a 21% premium over the purchase price paid purely in financing cost.

On a typical owner-operator truck loan in the current market, total interest paid over a 60-month term can represent 20 to 30% of the purchase price on top of what you owe for the truck itself. On a longer term or at a higher rate, it can exceed 35%. Those are not small numbers on a $75,000 purchase.

Why your first payment is almost entirely interest

Every standard truck loan uses amortization, which means the total debt is divided into equal monthly payments across the loan term. Each payment covers a portion of principal (the amount you borrowed) and a portion of interest (the lender's charge for lending it to you). The payment amount stays the same every month. What changes is the split between principal and interest inside each payment.

On the $65,000 loan at 9% APR, the monthly interest rate is 0.75% (9 divided by 12). In month one, your interest charge is 0.75% of $65,000, which equals $487.50. Your payment is $1,349. The principal paid in month one is $1,349 minus $487.50, which equals $861.50. Your outstanding balance after the first payment is $65,000 minus $861.50, which is $64,138.50.

You made a $1,349 payment and reduced the balance by $861.50. The other $487.50 went to the lender as the cost of having borrowed the money for that month.

In the early months of the loan, the outstanding balance is high. Because interest is calculated as a percentage of the outstanding balance, the interest component of each payment is large and the principal component is small. As you pay down the balance, the interest portion shrinks and the principal portion grows. By month 30, at the midpoint of the 60-month term, your outstanding balance is approximately $35,000. The monthly interest charge at that point is 0.75% of $35,000, which is $262.50. The principal portion of your payment has grown to $1,086.50. In the final month, nearly all of your payment is principal and the interest component is a few dollars.

RateGenius describes it this way: payments made toward a newer loan direct more money toward interest. As the term goes on, less and less goes toward interest and more goes toward paying down the balance.

The practical implication: you build equity slower than you think

If you sell the truck or trade it in two years into a five-year loan, you have paid two years of payments but reduced the principal balance by far less than two-fifths of the loan amount, because a disproportionate share of your first two years of payments went to interest. You have not built equity at the pace the payment count might suggest.

This is not a trick or a deception. It is the mathematical consequence of charging interest on an outstanding balance that is large at the start and small at the end.

What happens when you extend the term to drop the monthly payment

Extend the term to 84 months, which some lenders offer on commercial truck loans. The monthly payment drops to $1,031. Dealers love this conversation because the lower payment makes the purchase feel more affordable.

Here is what happens to the total cost. Over 84 payments of $1,031, you pay $86,604. Subtract the $65,000 principal and total interest paid is $21,604. The truck that cost $80,940 all-in at 60 months now costs $96,604 all-in at 84 months. You are paying $5,664 more to own the same truck and get a smaller monthly payment.

That trade is sometimes the right one for cash flow management. It should be made deliberately, with the total cost in front of you, not because the monthly payment felt more comfortable.

APR versus the stated interest rate: the gap that costs money

The annual percentage rate (APR) and the interest rate are related but not the same number, and the difference matters when comparing loan offers.

The interest rate is the cost of borrowing expressed as a percentage of the principal per year. It does not include fees. The APR includes the interest rate plus any lender fees, origination charges, and required costs of the loan expressed as an annualized percentage. By law, lenders must disclose the APR under the Truth in Lending Act, which makes it the correct comparison point between competing loan offers.

A lender advertising an 8.5% interest rate on a truck loan with a $1,500 origination fee and $500 in documentation charges has an effective cost higher than 8.5%. The APR, which includes those fees amortized over the loan term, might be 9.2%. Another lender advertising 9.0% with no fees has an APR of 9.0%. The first lender looks cheaper on the headline rate and is actually more expensive on a full-term comparison.

Several lenders in the commercial truck space advertise an interest rate rather than an APR. Always ask for the APR and always compare offers using APR on identical loan amounts and terms, not the monthly payment or the stated interest rate.

The Credit People's 2026 commercial truck loan guide adds the instruction to ask each lender for a full APR breakdown including all fees, then compare quotes side by side using identical down payment and term assumptions. A side-by-side APR comparison on the same loan structure eliminates the noise of different term lengths and fee structures that can make a more expensive loan appear competitive.

Why bigger loans often cost less per dollar borrowed

Lenders have fixed costs to underwrite, process, and service a loan regardless of its size. An origination review, a title search, document preparation, and ongoing servicing infrastructure cost roughly the same whether the loan is $15,000 or $75,000. On a $15,000 loan, those fixed costs represent a larger percentage of the loan amount, and the lender's margin on a smaller loan is thinner. Both factors push rates higher on smaller loan amounts.

The Credit People's current rate analysis confirms this dynamic directly: specialty lenders charge APRs between 7 and 12% or higher for sub-prime credit, with rates typically lower for larger loan amounts and strong collateral. Truckers Finance's 2026 owner-operator financing guide notes that operators in the prime bracket with two or more years in business see rates between 7 and 12%, while startup operations pay 15 to 22%, and the collateral value of the truck is a primary underwriting input.

In practical terms, an owner-operator financing a $15,000 truck at a specialty lender with limited credit history may be quoted 18 to 22% APR. The same operator financing a $65,000 truck with a stronger collateral position may qualify for 11 to 14% APR. The monthly payment on the more expensive truck is higher, but the total interest as a percentage of the loan amount is lower. The cost per dollar borrowed is less on the larger loan.

This does not mean buying a more expensive truck is always better. It means the assumption that a cheaper truck is automatically the lower-cost financial decision ignores the rate differential that financing cost creates at different loan amounts and collateral levels. Both scenarios need to be calculated on total cost, not purchase price or monthly payment.

How to run the calculation yourself

Every operator who finances equipment should run this calculation before signing. It requires four inputs and five minutes.

The first input is the financed amount, which is purchase price minus down payment. The second is the APR, confirmed in writing from the lender, not the stated interest rate. The third is the loan term in months. The fourth is a free online amortization calculator, of which dozens exist. The U.S. government's Consumer Financial Protection Bureau maintains a free loan calculator and a detailed explanation of amortization schedules. Any major bank or financial education site has a comparable tool.

Plug in the four numbers and the calculator produces three outputs: the monthly payment, the total amount paid over the full term, and the total interest paid. The total amount paid minus the principal equals the total interest. That is the number to compare across loan offers, not the monthly payment.

A concrete comparison between two offers on the same truck makes the method obvious. Offer A: $65,000 financed at 9.0% APR for 60 months. Monthly payment $1,349. Total paid $80,940. Total interest $15,940. Offer B: $65,000 financed at 10.5% APR for 60 months. Monthly payment $1,397. Total paid $83,820. Total interest $18,820. Offer B costs $2,880 more in total interest over the life of the loan. The monthly payment difference is $48. An operator focused only on the monthly payment might consider both offers essentially equivalent. An operator who ran the total interest calculation knows Offer A is $2,880 cheaper and takes Offer A.

What to do this week

Before you sign any truck loan, ask the lender for the APR in writing, not just the interest rate. Plug the financed amount, the APR, and the term into a free amortization calculator. Write down the total interest paid. Compare that number across every loan offer you get. The truck that costs $75,000 on the sticker might cost you $90,940 or $96,604 depending on the term and rate. Know which number you're signing up for.