Auto Rebate vs. Low Interest Financing Calculator
Dealers often make you choose between a cash rebate and a low promotional interest rate. This calculator works out which one actually costs you less.
A worked example
Running this tool on current national benchmarks (Federal Reserve / Freddie Mac via FRED (St. Louis Fed)) — swap in your own numbers to see how the result moves.
- Vehicle price
- $35,000
- Down payment
- $3,000
- Cash rebate
- $3,000
- Standard rate (with rebate)
- 7%
- Promotional low rate
- 2.90%
- Loan term (years)
- 5
saves $39 over the loan
- Rebate — payment$574.23
- Rebate — total cost$34,454
- Low rate — payment$573.58
How the cheaper option changes with vehicle price
Holding the other inputs at the example above, here is how the result moves as vehicle price changes.
| Vehicle price | Cheaper option | Rebate — payment |
|---|---|---|
| $20,000 | Take the rebate | $277.22 |
| $25,000 | Take the rebate | $376.22 |
| $35,000 | Take the low rate | $574.23 |
| $55,000 | Take the low rate | $970.26 |
| $70,000 | Take the low rate | $1,267.28 |
The math behind it
The calculator builds two loans on the same vehicle and down payment. The rebate path subtracts the cash rebate from the amount financed but charges your standard rate, since promotional financing and the rebate are usually mutually exclusive. The low-rate path finances the full price after down payment but at the promotional rate. Each loan is amortized over your term, and we compare total cost — principal plus all interest. The cheaper total wins.
Assumptions & limits
- The rebate and the promotional rate are treated as an either/or choice, which is how most manufacturer offers work.
- Both loans use the same down payment and term, so only the rebate and the two rates differ.
- The rebate is applied as a price reduction on the financed amount, not as cash back in your pocket.
- Sales tax, title, and dealer fees are excluded — add them equally to both sides since they do not change which option wins.
- Fixed rates are assumed for the full term.
Common questions
When is the cash rebate better than 0% or low-APR financing?
The rebate tends to win on shorter terms and smaller balances, where you would not have paid much interest anyway, so the up-front price cut matters more. Low-rate financing tends to win on longer terms and larger balances, where the interest you avoid outweighs the rebate. This calculator does the exact comparison for your numbers rather than relying on the rule of thumb.
Can I take both the rebate and the low rate?
Almost never. Manufacturer promotional rates are subsidized by the automaker in place of the rebate, so dealers present them as a choice. The calculator assumes you pick one. If a dealer genuinely offers both, take them — no comparison needed.
What standard rate should I enter for the rebate side?
Use the rate you would actually qualify for through your own bank, credit union, or the dealer's non-promotional financing — not the promotional rate. A credit-union pre-approval is a good source for a realistic standard rate, and it also gives you leverage at the dealership.