What it means
The back-end ratio is one half of a pair that lenders read together. The front-end ratio counts only housing costs against income, while the back-end ratio adds car loans, student loans, credit card minimum payments, personal loans and court-ordered obligations such as maintenance.
The income figure is gross, meaning before tax and deductions, which surprises borrowers who plan their lives from take-home pay. That is why a ratio that looks comfortable on a lender's screen can still feel tight in practice, particularly for people in higher tax bands.
What counts as debt is narrower than most people expect. Ongoing living costs such as groceries, utilities, childcare, insurance outside the housing payment and mobile phone bills are generally excluded, so the ratio measures contractual debt service rather than total outgoings.
Lenders set their thresholds by loan type and by how strong the rest of the application is. Ratios up to about 36% are treated as comfortable, many mainstream loans allow up to 43%, and some programmes stretch further where the borrower has a large deposit, substantial reserves or a long clean credit history.
The practical value of the ratio is in planning rather than in judging. If a borrower is above the cap, the useful levers are clearing a small balance entirely, refinancing a loan to reduce the monthly payment, adding a co-borrower with income, or simply targeting a cheaper property.
In practice
Real-world examples.
Example
A self-employed designer earning $7,500 a month gross applies for a mortgage with a $1,900 housing payment and $850 of other debt. Her back-end ratio is 36.7%, comfortably inside the cap, but the lender still asks for two years of accounts to confirm the income figure.
Example
A borrower fails at 45% and clears a $6,000 car balance with savings, removing a $520 monthly payment. The ratio drops to 39.2% and the application is approved without any change to the property or the deposit.
Example
A mortgage broker reviewing a client's file spots a $260 monthly instalment on a furniture plan that the client had not mentioned. Adding it moves the back-end ratio from 41% to 44%, so the pair agree to pay the balance off before the application is submitted.
Formula
Calculation
Back-end ratio = (Total monthly debt payments including housing / Gross monthly income) x 100
A couple applying for a mortgage have a combined gross income of $108,000 a year, which is $9,000 a month. The proposed housing payment covering principal, interest, property taxes and insurance is $2,160 per month.
Their other commitments are a car loan of $450, a student loan of $300 and credit card minimum payments of $190, so total monthly debt = $2,160 + $450 + $300 + $190 = $3,100.
Back-end ratio = $3,100 / $9,000 = 0.3444, or 34.4%. For comparison, the front-end ratio is $2,160 / $9,000 = 24.0%. Against a 43% cap, the lender would allow total debt payments of $9,000 x 0.43 = $3,870, so the couple have $3,870 - $3,100 = $770 a month of headroom, which is roughly how much extra mortgage payment they could take on before the ratio became a problem.Case study
Seen in the real world.
The Ellery household is a fictional example created to illustrate how the ratio behaves in practice. On a gross income of $11,000 a month they were confident about a $2,900 mortgage payment, because they had been saving successfully while renting a similar property for $2,650.
Their broker's calculation told a different story. Adding two car payments of $610 and $480, a personal loan of $340 and $220 of credit card minimums, total debt came to $4,550 a month, giving a back-end ratio of 41.4% against the lender's 43% limit. Technically they qualified, but with almost no room for the property taxes to rise or for a rate reset at the end of the fixed period.
They chose to spend six months paying off the personal loan and one of the cars before applying. Total monthly debt fell to $3,730, the ratio dropped to 33.9%, and they secured a better rate because the file moved into a stronger tier. The illustrative point is that the ratio is not only a gate to pass but a dial that changes the price of the loan.
Watch out
Common mistakes.
- Calculating the ratio on net take-home pay instead of gross income, which produces a much higher figure than any lender would use.
- Forgetting that the housing payment includes property taxes, insurance and any association fees, not just principal and interest.
- Assuming that scraping in under the cap means the loan is affordable, when the ratio ignores childcare, utilities, food and every other living cost.
Questions
People also ask.
What is the difference between the front-end and back-end ratio?
The front-end counts only housing costs against gross income, while the back-end adds every other monthly debt payment.
Do credit cards count at the balance or the minimum payment?
Lenders normally count the minimum monthly payment shown on the statement, not the full outstanding balance.
Can I be approved above 43%?
Sometimes, where compensating factors such as a large deposit, significant cash reserves or a very strong credit history support the file, though the pricing is usually less attractive.
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