The formula
Worked examples
How to calculate car loan
This is the /finance/loan/repayments calculation adapted for auto financing: the down payment and any trade-in are subtracted from the vehicle price first, and only the remaining balance is actually financed and charged interest.
A $32,000 vehicle with a $4,000 down payment and no trade-in leaves $28,000 financed. At 6.5% over a 5-year (60-month) term, that comes to a monthly payment of about $547.85, with total interest of roughly $4,871 over the life of the loan — about 17% of the amount financed.
Here is what each field means:
- Vehicle price
- Down payment
- Trade-in value — value of a vehicle you're trading in, subtracted from the amount financed
- Interest rate (%)
- Loan term (years)
The result updates on every keystroke. The URL updates too, which makes the filled-in version easy to bookmark or send to someone else.
Some of the fields above will accept figures that seem unusual for your own situation, and that is deliberate: the formula behind car loan works the same way regardless of scale, so the calculator does not stop you testing a hypothetical scenario a long way from your actual numbers — often the fastest way to see which input the result is most sensitive to.
Why car loan matters
A calculation like this usually gets used at a decision point rather than out of curiosity — comparing two real options, checking a number a lender or adviser has quoted, or working out whether a plan that sounded fine in conversation still holds up once it is written down with actual figures. The maths itself is rarely complicated; what is hard is remembering which figures to use and in what order, which is exactly what a dedicated calculator is for.
Beyond a one-off check, the same calculation is worth revisiting whenever the underlying numbers change — a new interest rate, a change in income, a different term. Because the figures live in the page's own web address, coming back to update just one field and compare the new result against the old one takes seconds rather than starting again from a blank page.
The reason a page like this exists at all, rather than leaving the calculation to a spreadsheet or a textbook appendix, is that the formula behind car loan is fiddly enough to get wrong by hand but not complicated enough to need specialist software. That middle ground — real enough maths to matter, simple enough to check instantly — is exactly what a dedicated calculator is for, and it is why the same figure recalculated here should match a careful manual calculation almost exactly.
Where the same calculation needs to be run for several different scenarios side by side — three loan offers, two savings plans — the fastest approach is usually to open the calculator in a second browser tab for each one, so that the results can be compared directly rather than overwriting each other in a single set of fields.
Worked example
Here is the calculation with the starting values:
- Vehicle price: 32,000
- Down payment: 4,000
- Trade-in value: 0
- Interest rate: 6.5 %
- Loan term: 5 years
That gives:
- Amount financed: 28,000
- Monthly payment: 547.85
- Total interest paid: 4,871.13
These figures are only the calculator's own starting values, included so the working is visible rather than hidden inside the tool above. Replace them with your own numbers and the same arithmetic applies — nothing about the method changes, only the inputs feeding it.
Reading the result
Every dollar of down payment or trade-in value reduces the amount financed — and therefore the interest charged on it — dollar for dollar. Raising the down payment on the example above from $4,000 to $8,000 cuts the financed amount to $24,000 and lowers both the monthly payment and total interest by roughly a seventh, not just by the size of the extra payment itself.
Where this goes wrong. Chasing a lower monthly payment by stretching the term. Extending the same $28,000 loan from 5 years to 7 drops the payment from about $547.85 to $415.78, but total interest rises from about $4,871 to roughly $6,926 — and a longer term also means more months where the car is worth less than the remaining loan balance (negative equity), since vehicles depreciate faster than a slow amortization schedule pays down the loan, especially with little or no down payment.
A useful check on any unfamiliar result is to compare it against a rough mental estimate first — round the inputs to convenient numbers and see whether the calculator's answer lands in roughly the same territory. A wildly different figure usually means one of the fields was entered in the wrong unit, most often a percentage typed as a whole number where a decimal was expected, or the reverse.
Yes, for this calculation — both reduce the amount actually financed before interest is calculated. Enter your trade-in's real market value rather than what a dealer initially offers, since trade-in offers are often negotiable and an inflated trade-in figure is sometimes offset by a worse price on the vehicle itself.
A longer term spreads the same balance over more monthly payments, which lowers each payment but means interest keeps accruing on a larger remaining balance for longer. Terms of 72–84 months have become common because they make expensive vehicles look affordable month-to-month, but they usually increase total interest paid and extend the period where the car is worth less than what's still owed on it.
It returns amount financed. With 32,000 vehicle price, 4,000 down payment and 0 trade-in value, that comes to 28,000. Change any field and the figure moves with it.
Whenever one of the underlying figures changes — a new interest rate, a different balance, an updated term — since the result only reflects what is currently in the fields. There is no need to keep a separate record of past results; the web address for a filled-in version already carries the figures used to produce it.
Not unless a tax rate or a fee is explicitly one of the inputs above. Where it is not, the figure shown is a gross calculation, and any tax due depends on your personal circumstances and current tax rules, which are worth checking separately.
The arithmetic itself is exact — the calculator applies the formula shown above precisely, with no rounding until the final figure is displayed. The uncertainty, where it exists, is entirely in the inputs: an estimated rate or an approximate balance carries that same approximation through to the result.