Over the past year, many Australians have discovered that even small interest rate increases can dramatically reduce how much they can borrow for a home loan.
When the Reserve Bank of Australia raises the cash rate, banks typically increase mortgage interest rates shortly afterwards. That impacts monthly repayments, mortgage stress levels, borrowing capacity, and loan approval chances.
What surprises many borrowers is that borrowing power often falls faster than repayments rise. Australian lenders assess home loans using stricter serviceability rules—including the APRA assessment buffer and minimum living expense benchmarks—so the numbers you see on a basic repayment calculator do not tell the whole story.
What happens when interest rates rise?
When mortgage rates increase, your monthly repayments typically become higher. Banks also assess your loan at a higher stress-test rate than your contract rate, which reduces the surplus income available for new borrowing. Together, that lowers how much a lender may approve—even before other debts or expense floors are applied.
- Monthly repayments rise for variable-rate loans (and eventually for many fixed loans after rollover).
- Lenders assess affordability using a buffered assessment rate, not just your current repayment.
- Your surplus income shrinks on paper, so borrowing power drops.
- Loan approval depends on policy-specific limits, not a single national formula.
For example, a borrower on a 6.0% contract rate may be assessed closer to 9.0% once the common contract rate plus 3% style buffer is applied. That means even a modest rate increase can materially change the loan size a lender is willing to approve.
Real borrowing power examples (indicative)
The table below illustrates how sensitive borrowing capacity can be to the rate used for assessment. These figures are illustrative only and will change with expenses, debts, household type, and lender policy.
| Household income | Approx. borrowing @ 5.5% | Approx. borrowing @ 6.5% |
|---|---|---|
| $120,000 | $760,000 | $660,000 |
| $180,000 | $1,180,000 | $1,020,000 |
| $250,000 | $1,720,000 | $1,500,000 |
These figures depend on existing debts, credit card limits, dependants, living expenses, rental income, and loan structure. For a personalised view, use our borrowing power calculator.
Why borrowing power can fall faster than expected
Many borrowers assume that if variable rates rise by 1%, borrowing power should only dip slightly. In practice, lenders stack multiple constraints: buffered assessment rates, minimum living expense floors, and existing commitments—each can shrink capacity on its own.
APRA serviceability buffer (how banks stress-test)
Australian banks typically assess borrowers at a higher rate than the loan's contract rate. A widely referenced rule of thumb is actual interest rate plus 3%. So if your mortgage rate is 6.2%, borrowing capacity may be assessed closer to 9.2%. That tests whether you could still afford repayments if rates rise further—before other policy overlays.
Our borrowing power calculator applies an APRA-style assessment buffer on top of your entered rate so you can see one realistic capacity envelope.
HEM-style living expense benchmarks
Lenders also apply minimum living expense benchmarks (often described as HEM-style floors). Even if you declare low expenses, the bank may use a higher benchmark based on household type, dependants, and internal policy. Where the benchmark exceeds your declared expenses, assessed surplus falls—and so does borrowing power.
Important caveat
Published tables and calculators cannot replicate every lender's credit policy. Treat any estimate as indicative and confirm with your broker or lender before making decisions.
How much can rate rises increase repayments?
On a principal-and-interest loan, repayment sensitivity depends on balance, remaining term, and how rates move. The table below shows approximate monthly repayment increases for a 1.0 percentage point rate rise on selected loan sizes—use our mortgage calculator for your exact loan amount, rate, and frequency.
| Loan amount | Rate increase | Approx. monthly increase |
|---|---|---|
| $600,000 | +1.0% | +$390/month |
| $800,000 | +1.0% | +$520/month |
| $1,000,000 | +1.0% | +$650/month |
Multiple consecutive increases compound the cashflow impact over a year. Modelling scenarios early helps you align your budget with both contract repayments and lender assessment constraints.
What can you do if borrowing power has dropped?
Some borrowers improve assessed capacity by reducing unused credit limits, paying down personal loans, increasing deposit size, tightening discretionary expenses, applying jointly, or restructuring existing debts. Each lender weighs these factors differently.
Remember upfront costs still matter for purchasing power: NSW stamp duty and other settlement costs affect how much cash you need at completion alongside your loan.
Try our Australian mortgage calculators
Use these tools together to connect repayment cashflow, borrowing capacity, and purchase costs.
Frequently asked questions
- Why does borrowing power fall when rates rise?
- Higher rates lift repayments in servicing calculations and reduce surplus income. Lenders also apply a buffered assessment rate, so capacity often declines by more than a simple repayment change suggests.
- What is the APRA serviceability buffer?
- It is an additional margin applied when testing whether you can afford repayments under higher rates. A common illustration is assessing loans near contract rate plus 3%, though policies differ by lender.
- How much do repayments increase after a rate rise?
- It depends on loan size, term, and product. Use the mortgage calculator with your balance and rate to estimate monthly repayment movement for your situation.
- Do all banks calculate borrowing power the same way?
- No. Credit policies vary by lender on buffers, expense benchmarks, income shading, and debts—two lenders can produce meaningfully different outcomes for the same application.
Related guides
More guides will appear here as we publish them. For now, explore the calculators above or return to latest guides on the homepage.