Example result based on the prefilled values.
Monthly Payment
A$916.67
Total Interest
A$275,000.00
Capital Due
A$200,000.00
Continue your plan
Useful next calculations
When to use this calculator
- Before comparing lenders, brokers, or repayment options.
- When you want to test how a different deposit, rate, or term changes affordability.
- When you need a quick estimate before using a formal quote or agreement in principle.
- When you are stress-testing your budget against a potential rate rise to see the impact on monthly payments.
- When you want to understand the full cost of borrowing — not just the monthly figure — before you commit.
A realistic Australia planning example
Use these sample inputs as a quick scenario test, then change one variable at a time to compare outcomes.
Loan Amount (A$)
A$560,000
Interest Rate (%)
5%
Term (Years)
25 years
After entering these figures, review monthly payment, total interest and capital due together rather than in isolation — each metric tells a different part of the story. Then rerun the tool with one input adjusted to see which variable has the biggest effect on all three outputs before you settle on a plan.
How to read your results
Monthly Payment
Use this to check whether the scenario fits comfortably within your regular budget. If it looks tight, rerun the tool with a longer term or larger deposit to find the boundary of affordability.
Total Interest
This shows the long-run cost of borrowing beyond the original principal, which is especially useful when comparing terms or weighing up overpayment options. A shorter term usually cuts this figure significantly even if the monthly payment rises.
Capital Due
Use this metric to compare scenarios side by side and understand how changes in the key inputs drive the final outcome. If the figure surprises you, isolate one variable at a time and rerun the calculation to identify which assumption is responsible.
Method & assumptionsAuthoritative sources
An interest-only mortgage means your monthly payment covers only the interest charged on the outstanding loan — the original capital remains unchanged throughout the term and must be repaid in full at the end. This calculator computes the monthly interest charge by applying the annual rate (divided by 12) to the full loan balance, which remains constant because no capital is being repaid. In practice, the interest rate on your mortgage will likely change over time as fixed or tracker periods end and you remortgage, so the real cost will fluctuate. The calculator does not model the performance of any associated repayment vehicle. UK lenders require a verified, independent repayment strategy before granting an interest-only loan; the FCA mandates regular contact between lenders and borrowers to monitor repayment plans throughout the mortgage term.
Common mistakes
- !Using an assumption that is not supported by a current local quote, bill, statement or official source.
- !Treating a generic estimate as a lender, provider, payroll or tax authority decision.
- !Mixing monthly and annual inputs without converting them consistently.
- !Forgetting location-specific taxes, fees, eligibility rules or payroll deductions where they apply.
- !Testing only one scenario instead of checking how a cautious assumption changes the result.
What to do next
- Run a second scenario with a cautious assumption so you can see the downside clearly.
- Compare the result with the related calculators below before making a decision.
- Check current local rules, eligibility and provider terms before applying or committing money.
- Keep a record of the assumptions so you can update the estimate when a quote, bill or pay figure changes.
- Use the result to prepare better questions for a lender, provider, adviser or employer rather than treating it as a final answer.
Frequently asked
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