How to use the Cash Back vs Low Interest
- Enter the negotiated vehicle price, agreed before discussing incentives.
- Enter the cash rebate offered.
- Enter the rate you would pay if you take the rebate, and the promotional rate available instead.
- Set the term and read which option costs less in total.
How the calculation works
A rebate reduces the amount financed immediately, while a low rate reduces the cost of carrying it. Which dominates depends on the term: short terms favour the rebate because there is little interest to save, and long terms favour the subsidised rate because the interest differential compounds over more months.
The comparison is only valid if the vehicle price is identical in both scenarios. Negotiate the price to a fixed number first, then reveal which incentive you are considering — otherwise the dealer can move the price to neutralise the comparison.
Promotional rates are typically restricted to top-tier credit and to specific in-stock trims. If you do not qualify, the effective choice is rebate versus standard financing, which the rebate wins by definition.
Cost A = PMT(r_std, n, price − rebate) × n; Cost B = PMT(r_promo, n, price) × nSource: Federal Reserve G.19 new car loan rate series; standard manufacturer incentive structures documented by NADA.
Worked example
$35,000 vehicle, $2,500 rebate at 7.9%, versus 1.9% promotional financing, 60 months.
- Rebate path finances $32,500 at 7.9% — about $657 a month, $39,400 total.
- Low-rate path finances $35,000 at 1.9% — about $612 a month, $36,700 total.
The promotional rate wins by roughly $2,700 over the term at this rate gap.
Frequently asked questions
Can I get both incentives?+
Almost never — manufacturers present them as alternatives precisely because their cost to the maker is similar.
What if I plan to pay cash?+
Take the rebate. With no financing, a subsidised rate is worth nothing.
Does a trade-in change the answer?+
It reduces the amount financed on both sides equally, which slightly favours the rebate as the balance shrinks.
Last reviewed September 1, 2026. We review this page whenever the underlying formula, tax year, published rate or standard changes.