How a Credit Card Limit Cuts Your Borrowing Power

The short answer

As a rule of thumb, every $1,000 of credit card limit cuts your home loan borrowing power by roughly $5,000-$6,000, so a $10,000 limit can knock around $50,000-$60,000 off the amount a lender will approve. The part that surprises most people is what gets counted: lenders assess your full approved limit, not your current balance, so a card you've paid down to zero still drags your capacity down. Reducing or closing a card before you apply is one of the fastest ways to lift your borrowing power without earning more.

How it works in Australia

When a lender works out how much you can borrow (your "serviceability"), it adds up your income, subtracts your living expenses and existing debt repayments, and applies a stress test. Two rules drive the credit card effect.

• Limit, not balance. A credit card is a revolving facility, and you could draw the whole limit tomorrow. So lenders treat the entire approved limit as a potential debt and apply an assumed minimum monthly repayment to it, typically around 3% to 3.8% of the limit per month. On a $10,000 limit that's roughly $300-$380 a month of "phantom" repayment, even if you never carry a balance.

• The serviceability buffer. APRA requires lenders to test whether you can still afford the loan if interest rates rose. The buffer has stayed at 3 percentage points above the loan rate (APRA macroprudential settings). So a 6% loan is assessed at around 9%. Because every dollar of committed expense is magnified through this stressed rate, a few hundred dollars of assumed card repayment translates into tens of thousands of dollars less loan.

That combination is why the impact feels so disproportionate to a small plastic card.

Worked example

Take a buyer assessed on a 6% loan rate, stress-tested at 9% (the 6% rate plus APRA's 3% buffer) over a 30-year term.

The lender treats a credit card as costing about 3.8% of the limit per month. So a $10,000 limit adds an assumed $380/month liability to the serviceability sum.

How much loan does $380/month "buy" at the 9% assessment rate over 30 years? The present value of $380 a month for 360 months at 9% p.a. works out to roughly $47,000. In other words, that $10,000 card limit consumes about $47,000 of borrowing capacity, right inside the $50k-$60k rule-of-thumb range. Scale it:

Credit card limit	Assumed monthly repayment (3.8%)	Approx. borrowing power lost
$5,000	$190	~$24,000
$10,000	$380	~$47,000
$15,000	$570	~$70,000
$25,000	$950	~$118,000

The same $47,000 gap matters at settlement too. On a standard $600,000 loan at 6% over 30 years, the monthly repayment is about $3,597. Losing $47,000 of capacity could push a purchase below 80% LVR, change whether LMI applies, or affect which first-home concessions you qualify for.

Model this in True Loan

True Loan is a free calculator and doesn't run a lender's full serviceability test, but you can see the consequence of a smaller approved loan directly:

1. Open the calculator at trueloan.app and enter your loan amount, interest rate, and term.
2. Set up Scenario A with the loan you hoped for, and Scenario B with that figure reduced by the capacity your card consumes (e.g. $47,000 less for a $10,000 limit), then use the comparison tool to see both side by side.
3. Compare the repayments, total interest, deposit and upfront costs between the two, including how a lower loan changes your LVR and whether LMI kicks in.

If you're thinking about funnelling spare cash into the mortgage instead of holding a large card limit, the dedicated Offset balance input models a sustained offset, while the separate Extra repayment ($/month) input models regular extra payments. They're two different levers in True Loan.

Common questions and mistakes

Does paying my card to zero each month fix it? No. Lenders assess the limit, not the balance or your repayment habits. A $20,000 limit you never use still counts as a $20,000 facility.

Should I just close the card? That's a personal call. Closing or lowering a limit before applying generally lifts capacity, but it can also affect your credit profile and convenience. This is general information, not advice; speak to a licensed broker or lender.

Is it always 3.8% of the limit? No. Different lenders assume different percentages (commonly 3% to 3.8%/month), and some use slightly different buffers, so your real number will vary. Treat the table above as a guide.

Do other debts work the same way? Personal loans, car loans (HECS/HELP) and "buy now, pay later" facilities are assessed on their actual repayments, but undrawn lines of credit behave like cards: the limit counts.

A note on the figures

These numbers are estimates to show how the mechanics work, not a quote of what any lender will approve. Serviceability rules, assumed repayment percentages and the APRA buffer vary by lender and change over time, so check current rules with the lender, a licensed broker, and moneysmart.gov.au. This is general information only and not financial or credit advice.