Cash Back or Low Interest Calculator

Two offers, one question

A car dealer rarely offers a rebate and a low rate on the same car. The manufacturer puts money behind one or the other, and you pick. The question is not which sounds better, it is which one leaves you with less cash out the door after the last payment.

That means adding up everything: the down payment, every monthly payment for the full term, and the effect of the rebate on the amount you borrow. The offer with the smaller total wins, and the difference is often four figures.

The comparison is not close to obvious, because the two offers move in opposite directions. A rebate cuts the principal, which cuts both the payment and the interest. A low rate leaves the principal alone and cuts only the interest. Which one wins depends on how much interest the rate would have charged, and that depends on the rate, the term and the size of the loan.

On a $30,000 car with $3,000 down, a $2,000 rebate against 0% financing over 60 months, the low rate wins by $3,085. Change the term to 36 months and the gap narrows to $1,012. Change the rebate to $5,000 and the rebate wins by $525. The calculator exists to run those variations before you sit at the desk.

The math: compare total cash out

Both offers are loans with the same price, the same down payment and the same term. Only two things differ: the amount financed and the rate.

• Rebate deal. Amount financed is price minus down payment minus rebate. Rate is the standard rate you qualify for.
• Low rate deal. Amount financed is price minus down payment. Rate is the promotional rate, which is often 0% and sometimes 1.9% or 2.9%.

The monthly payment comes from the standard amortization formula: principal times the monthly rate, divided by one minus one plus the monthly rate to the negative power of the term. For a 0% loan the payment is principal divided by the number of months.

Total cash out is the down payment plus the payment times the term. That total is the only fair comparison, because it captures the rebate and the interest in one number. Monthly payment alone hides the difference: a longer term lowers both payments and makes the two offers look closer than they are.

One subtlety worth knowing: the rebate reduces the amount financed, so it also reduces the sales tax base in most states. That makes the rebate slightly more valuable than the sticker number suggests, by roughly the sales tax rate times the rebate. The calculator leaves tax out to keep the comparison clean, so treat a small extra edge on the rebate side as real.

Worked example: $30,000 at 7.54% against 0%

A $30,000 car, $3,000 down, a $2,000 rebate, a standard rate of 7.54% and a promotional rate of 0%, both over 60 months.

The rebate deal looks better on the sticker, because you borrow $2,000 less. It loses on the payment, because 7.54% on $25,000 costs $5,085 over five years, which is more than the $2,000 you saved. The 0% offer wins by $3,085 and also has the lower monthly payment, so there is no trade-off to weigh.

Now move the rebate to $5,000 and the picture flips. The rebate deal finances $22,000 at 7.54%, which is $441.29 a month and $26,477 in total payments. Add the $3,000 down and the cash out is $29,475, which beats the 0% offer by $525. The crossover sits at a rebate of $4,564.

The break-even rebate

The break-even rebate is the amount that makes the two offers cost exactly the same. Above it, take the rebate. Below it, take the low rate. It is the single most useful number in this comparison, because it turns a vague choice into a threshold you can check against the dealer's offer.

The formula is the loan amount times one minus the ratio of the two payment multipliers. In plain terms, the low rate offer is worth whatever extra interest it saves, and the rebate has to beat that number to win. A 0% loan on $27,000 over 60 months saves $5,085 in interest, but the rebate also shrinks the principal, so the true threshold lands lower, at $4,564.

Read the table the other way and it says something useful about shopping: the worse your credit, the bigger the rebate has to be to beat a promotional rate. At 11% the threshold is $6,303, which few rebates reach. At 5% it is $3,154, which many do.

A promotional rate of 1.9% instead of 0% drops the threshold to $3,464, because the low rate offer now carries $1,324 of interest of its own. Every point of promotional rate is worth real money on the rebate side.

Term length changes the answer

The same two offers produce different winners at different terms, and the pattern is consistent: the longer the loan, the more the low rate is worth. Interest has more time to accumulate on the standard-rate loan, so the rebate has to be larger to compensate.

The 36-month row is where a $2,000 rebate comes closest to winning: the gap is only $1,012. At 84 months the same rebate loses by $5,252. Long loans punish the standard rate, which is why dealers like to stretch the term when the manufacturer is pushing a rate incentive.

There is a second effect in the payment columns. At 84 months the two payments are $384 and $321, a difference of $63 a month that feels small. Over 84 months it compounds into $5,252. Monthly payment is the number the dealer quotes and the worst number to compare with.

What the promotional rate hides

A 0% offer is a real discount, but the terms around it usually carry conditions that the headline does not mention.

• Credit requirements. Promotional rates often go to the top credit tier only. If you land one tier lower, the rate can jump to 5% or more, and the offer you compared is not the offer you get.
• Shorter terms. Many 0% programs cap at 36 or 48 months. A 36-month 0% loan on $27,000 is $750 a month, which is a budget decision as much as a math one.
• Lost rebate. The two incentives usually come from the same budget, so taking the rate means giving up the cash.
• No early payoff benefit. On a 0% loan there is no interest to save by paying early, so the flexibility of an early payoff is worth less than it is on a standard loan.
• Price negotiation. Some programs restrict how far the dealer can discount below sticker. Ask whether the price changes if you decline the promotional rate.

The reverse also holds. A rebate can be combined with an outside loan from a credit union or a bank, and those rates are sometimes close to the promotional rate. When they stack, the rebate deal can win comfortably. Ask the finance office both questions in the same conversation: what is the price with the rebate, and what is the rate without it.

When the rebate wins

The rebate wins in four situations, and they are easy to spot once you know the threshold.

• The rebate is large. Above the break-even number, which is roughly 17% of the loan amount at 7.54% over 60 months, the rebate is the better deal at any term.
• The loan is short. At 24 to 36 months there is little time for interest to build, so a modest rebate can beat a 0% rate.
• You pay off early. Interest is charged on the outstanding balance, so a payoff at 18 months leaves the rebate intact and cuts most of the interest. Run the comparison at your planned payoff month, not at the full term.
• The promotional rate is not that low. A 2.9% or 3.9% offer is worth much less than 0%, and a mid-size rebate often beats it.

The rebate also wins on flexibility. Cash in hand can go toward the down payment, an emergency fund or a higher-yield debt, while a rate discount only exists inside the loan. If you are choosing between a rebate and a 1.9% rate and the numbers are close, the cash is the safer asset.

One caution: never let the incentive decide the car. Both offers apply to the same vehicle, so the comparison is only valid after you have negotiated the price as if neither incentive existed. Get the out-the-door price first, then choose the incentive.

Where the numbers come from

The default standard rate in the calculator is 7.54%, which is the average rate on a 60-month new car loan at commercial banks in August 2026, from the Federal Reserve's G.19 Consumer Credit release dated October 7, 2026. The 72-month average in the same release is 7.17%. Those are averages across all borrowers, so your own rate will depend on credit score, term, lender and the age of the car.

The promotional rate is set by the manufacturer and changes monthly, so the calculator defaults to 0% and lets you enter whatever the dealer quotes. The CFPB auto loan worksheet is a useful companion, because it walks through the same comparison in writing and asks for the total cost rather than the monthly payment.

Treat the result as a planning estimate. It ignores sales tax, title, registration, dealer fees, insurance differences and any add-ons rolled into the loan, and it assumes the rate holds for the full term. Those items land on both offers and rarely change the winner, but they do change the total, sometimes by more than the incentive itself.

This is a comparison tool, not financial advice. Confirm the actual rate, term and rebate in the finance contract before you sign.