Use the same car and the same offer date
A manufacturer often lets you choose between two mutually exclusive deals on the same new car: a cash rebate that lowers the price, or a below-market interest rate. This page compares them fairly by putting both through one purchase ledger. Enter the vehicle price, your cash down payment, any trade-in, the sales tax rate and the fees once, and they apply to both offers. Then enter each offer's own rate, term and rebate. Because the car and the fees are identical, any difference in the result comes from the offers themselves.
Use quotes you can actually obtain on the same day. A promotional rate that requires excellent credit is not an offer you can compare against if you do not qualify, and a rebate may depend on the model, the region or the date. If you only have a lender's pre-approved rate for the cash-back option, enter that rate as offer A and the promotional rate as offer B. This page is about car financing; credit-card rewards and similar cash-back programs are a different subject.
How cash back changes the purchase ledger
A rebate reduces the amount you need to finance dollar for dollar, which is why it lowers the monthly payment and the interest. In the ledger, the financed principal is the price minus the rebate, minus your down payment and trade-in credit, plus any trade debt, plus whichever of tax and fees you choose to finance. The rebate is not a separate payment; it is a reduction in the balance that your interest rate then applies to.
Whether the rebate also reduces the taxed amount depends on where you buy, so the page has a switch rather than an assumption. With the switch off, tax is computed on the full price. With it on, tax is computed on the price minus the rebate, which lowers tax by the tax rate times the rebate. Another control lets you type the taxable base from your paperwork, which overrides both. Because both offers use the same tax rule, the rule changes the size of the difference, and it can sometimes change which offer wins.
One practical consequence is that a rebate applies to a smaller loan for the whole term, so its effect on interest is real but modest, while its effect on cash is immediate. Taking the rebate as cash toward the down payment, instead of letting it reduce the financed amount, produces the same principal in this model, so the page does not need a separate setting for that choice.
Compare complete costs, not interest alone
The headline question is which offer costs less in total, so the verdict uses total cash outlay: the cash you pay at signing plus every monthly payment. Interest alone can mislead. The low-rate offer pays less interest, but the cash-back offer starts with a smaller loan, so a comparison of interest ignores the rebate that produced it. Comparing outlay puts both on the same footing, because it counts every dollar leaving your pocket over the life of the loan.
The page also avoids a rounding trap. It subtracts the unrounded outlays and then shows the difference, instead of subtracting two rounded monthly payments multiplied by the number of months. When the two totals are within one cent the page reports a tie rather than naming a winner. If the terms of the offers differ, the full-term totals cover different periods, so the page says so and points you to the early settlement comparison, which measures both offers at the same month.
Think of the two offers as two different ways to pay for the same car. The rebate is a one-time discount that you receive up front. The low rate is a stream of savings that arrives month by month, and its total depends on how large the loan is and how long you keep it. A low rate saves more when the loan is big and the term is long; a rebate is worth more when the loan is small, the term is short or the rate gap between the offers is narrow. That is why the same pair of offers can change places when you change the price, the down payment or the term. A larger down payment, for example, shrinks the loan on which the low rate works, which tends to favor the rebate, while a longer term does the opposite. Run the comparison with the figures you will actually use, not with an example from an advertisement, and rerun it if the seller changes the price.
Worked rebate-versus-low-rate comparison
Start with a 50,000 car, 10,000 down, 7% sales tax and 2,000 of fees, all paid at signing, over 60 months. Offer A is a 5% loan with a 1,000 rebate. Offer B is a 2% loan with no rebate. Offer A finances 39,000.00 at 735.98 a month and has a total cash outlay of 59,658.69. Offer B finances 40,000.00 at 701.11 a month and has a total cash outlay of 57,566.62.
The low rate wins by 2,092.06, computed from the unrounded totals. Interest explains the gap: offer A pays 5,158.69 of interest against 2,066.62 for offer B, a difference of about 3,092, and the 1,000 rebate recovers only part of it. Now raise the rebate on offer A to 4,000. Offer A's outlay falls to 56,261.86 while offer B stays at 57,566.62, and the cash-back offer wins. The same model, with one number changed, flips the answer, which is why a rule of thumb about which offer is better is unreliable.
You can use the result in two ways. If you are certain which offers are available, read the verdict and the outlay difference directly. If you are negotiating, treat the difference as a target: the low rate saves 3,092 in interest, which is 2,092 more than the 1,000 rebate is worth, so a seller who wants you to take the rebate has to raise it by roughly that amount before the two offers match. Notice also that the monthly payments differ by only 34.87, which looks small in any single month but accumulates over 60 payments. The page keeps the monthly figures visible but bases the verdict on total outlay so that this accumulation is not missed, and it reports a tie rather than a winner when the totals are within a cent.
Taxes, trade debt and financed fees
Three entries shape how the two offers compare beyond the rate and rebate. Sales tax changes the price-related part of the ledger, and the rebate switch decides whether the tax base shrinks. Trade-in value and trade debt enter both offers equally, so they change the loan amount but not the logic of the comparison. Fees can be common to both offers, and you can also give each offer its own extra fee, financed or paid at signing, for a loan that carries a charge the other does not.
The page includes a small table that runs the same entries with the rebate switched between not reducing and reducing the taxable price, with tax financed. In the default example, the rebate switch moves offer A's outlay from 60,121.65 to 60,042.39. The table shows the result under each treatment so you can see whether your decision depends on the rule. It does not tell you what the rule is where you live; check the purchase paperwork and, if needed, type the taxable base yourself.
Fees deserve the same care as tax. If one lender charges an origination fee and the other does not, enter it as that offer's own fee and choose whether it is financed. A fee that is financed accrues interest for the whole term, so it costs more than the same fee paid at signing. Trade debt works the same way for both offers: it increases the amount financed under either one, so it enlarges the loan on which the low rate acts and tends to favor the lower rate.
Break-even rebate and early settlement
The break-even rebate answers a negotiating question: how large would the rebate on offer A need to be to make the two offers cost the same, holding everything else fixed? The page finds it by repeated halving between zero and the largest rebate the purchase can absorb, and it checks the result to within one cent of outlay. In the default example the break-even rebate is 2,847.66. A rebate below that favors the low rate; above it favors the cash back. If no rebate can equalize the offers, the page says so instead of showing a number.
Many people do not keep a car loan to the end, so the early settlement comparison measures both offers at the same month. It adds the cash at signing, the payments made through that month and the balance still owed afterwards, plus any penalty you enter. In the example, settling after 12 payments costs 56,290.08 under offer A and 56,229.82 under offer B; after 36 it is 58,771.02 and 57,221.08; at the full 60 months it is 59,658.69 and 57,566.62. Comparing at the same date is what makes the check fair.
Use the break-even rebate as a negotiating number rather than a prediction. If the rebate on offer is above it, taking the rebate costs less under your assumptions; if it is below, the low rate wins. Because the calculation holds everything else fixed, change any assumption, such as the term or the down payment, and calculate again, because the break-even moves with them. A very short horizon also shifts the answer toward the rebate, because the rebate is received at once while the interest savings of the low rate have little time to accumulate, which is exactly what the early settlement table lets you check.
Offer limits, eligibility and next steps
This tool compares mutually exclusive offers. It does not know whether you qualify for the promotional rate, whether a rebate can be combined with special financing, or what a lender will actually charge you. It assumes fixed rates and equal monthly payments, no introductory rate that resets, no refinance later and no tax deduction for interest. The early settlement penalty is a number you type; the page does not look up any lender's policy. Treat the verdict as arithmetic on the offers you entered.
Before you choose, check the monthly payment against the rest of your finances. To see whether the payment fits your income and other costs, check the affordable car budget. If you are weighing a new car against a used one, compare new and used ownership costs before the financing decision. If you already have a car loan and might pay it off early, calculate an existing auto-loan payoff. For the full purchase ledger with a schedule, use the auto loan calculator.
Be careful about the conditions attached to each offer. Promotional rates are often limited to certain models, terms or credit profiles, and rebates may require you to finance through a particular lender or may not be combinable with other discounts. The calculator cannot see those conditions, so confirm them before relying on a result. Also consider what you will do with the money you save: a comparison assumes the cash you do not spend on interest is simply saved, and it does not credit you with any return on the rebate you received up front. If you can invest that money at a meaningful return, the rebate looks slightly better than this page shows. Finally, keep a copy of both written offers and compare the final contract with the figures you entered here before you sign anything.
FAQ
Should I take cash back or low APR?
Compare the complete modeled outlay under offers you can actually obtain. The result depends on price, rebate, interest, term, tax and fees; a smaller payment alone is not decisive.
Is the rebate always deducted before sales tax?
No universal treatment is assumed. Set the rebate tax-credit control or enter the taxable base from the transaction paperwork.
What if I will pay the loan off early?
Use the same settlement month for both offers. Include payments already made, debt still owed and any entered penalties.
What does break-even rebate mean?
It is the feasible rebate that makes total modeled outlay equal to the low-rate offer under the other entered assumptions.
Can I combine the rebate with promotional financing?
Only if the actual offer permits it. This calculator compares mutually exclusive offers and does not determine promotional eligibility.