Car Loan Debt-to-Income Calculator

The calculation itself

Debt-to-income is total monthly debt payments divided by gross monthly income. The car version adds the proposed payment to what you already owe and expresses the result as a percentage.

Run in reverse it gives the more useful number: the largest payment that keeps you inside a target, which is income × target − existing debt.

It is the ratio the lender computes, which is why computing it first changes the conversation. You arrive with a payment and the arithmetic behind it rather than being asked what payment you would like.

In practice

$6,000 a month gross with $700 of existing debt payments is a current ratio of 11.7%.

Add a proposed $520 car payment and it becomes 20.3% — comfortably inside a 36% limit.

At that limit the largest payment available is $6,000 × 0.36 − $700 = $1,460, so there is $940 a month of headroom above the proposed payment.

That headroom is what a lender sees. It is not what your budget sees, because insurance and fuel do not appear in this ratio at all.

What counts and what does not

Counted: minimum payments on credit cards, other loan and lease payments, student debt, and rent or mortgage where applicable.

Not counted: insurance, fuel, utilities, groceries, childcare, subscriptions. None of them are optional and all of them compete for the same money.

That exclusion is the reason a DTI within target can still be a purchase you cannot afford, and it is why the affordability calculator on this site subtracts running costs before sizing the loan while this one does not — they answer different questions, and the lender only asks one of them.

Where the figure deceives

There is no universal threshold. 36% is common, 43% appears frequently, and strong applicants clear more. It varies by lender and interacts with credit history and the loan-to-value on the vehicle, so treat the target here as a setting rather than a rule.

Gross income flatters the ratio for anyone with a high effective tax rate. The same 36% on gross can be well over half of take-home.

And a low ratio is not an approval. It is one input among several, and vehicle age, term and credit history all weigh in — it helps, and a high ratio is hard to overcome, but neither settles it.

Acting on it

Calculate it before applying, and if it is tight, reduce a balance with a large minimum payment. That moves the ratio more than the balance size suggests.

A larger deposit lowers the payment and therefore the ratio, and is usually easier to arrange than removing an existing debt.

Then check the same purchase against take-home pay and actual running costs. The lender's ratio is the one that decides approval; the other one decides whether the next three years are comfortable.