Australian Mortgage Calculator

Use this skill as a guidance-only framework for Australian home-loan affordability planning.

Use this skill when

• The user needs repayment and affordability estimates.
• The user wants deposit and LVR scenario comparisons.
• The user needs a structured checklist of likely upfront costs.

Do not use this skill when

• The request is unrelated to personal mortgage planning.
• The user expects lender-grade approval decisions from this skill.

Guardrails

• Treat outputs as estimates, not financial advice.
• Always tell users to verify current rates, duties, grants, and lender policy for their state.
• Do not present outdated government incentive figures as guaranteed.

Core calculations

1) LVR (Loan-to-Value Ratio)

LVR = (Loan Amount / Property Value) × 100

2) Principal and Interest repayment (monthly)

M = P × [r(1+r)^n] / [(1+r)^n - 1]

Where:
P = loan principal
r = monthly interest rate (annual rate / 12)
n = total months (loan term × 12)

3) Interest-only repayment (monthly)

Monthly IO = Principal × (Annual Rate / 12)

Planning workflow

1. Collect buyer inputs

   • Property price target
   • Deposit amount
   • Loan term and expected interest rate
   • State/territory
   • Existing debts and household context

2. Run scenario comparison

   • Baseline (current deposit)
   • Lower deposit scenario (higher LVR)
   • Higher deposit scenario (lower LVR)
   • Optional stress scenario (interest rate +1% or +2%)

3. Estimate upfront cost buckets

   • Stamp duty (state dependent; verify latest schedule)
   • LMI likelihood if LVR exceeds common thresholds
   • Legal/conveyancing, inspections, and setup fees

4. Assess repayment comfort

   • Compare repayment estimate to user’s budget buffer.
   • Highlight risk if repayments exceed comfort threshold.

5. Summarize actions

   • What to verify with broker/lender
   • Which scenario appears most sustainable
   • Key risks and mitigations

Output format

## Home Loan Inputs
- Property value:
- Deposit:
- State:
- Interest rate assumption:
- Loan term:

## Scenario Comparison
| Scenario | Loan Amount | LVR | Monthly P&I | Monthly IO | Notes |
|---------|-------------|-----|-------------|------------|------|
| Base | | | | | |
| Lower deposit | | | | | |
| Higher deposit | | | | | |

## Upfront Cost Checklist (Estimates)
- Stamp duty (verify current state rates):
- LMI likelihood/cost range:
- Legal/conveyancing:
- Inspections and miscellaneous:

## Affordability and Risk Notes
- Repayment comfort assessment:
- Sensitivity to rate rises:
- Main risks:

## Next Steps
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