How To Stress-Test a $2–5m Eastern Suburbs Mortgage Properly

You should stress-test a $2–5 million Eastern Suburbs mortgage by modelling (1) rates 3% higher than today and (2) at least a 30–50% drop in variable income, then checking whether your repayments stay under ~30–35% of after‑tax household income and your cash buffers cover 6–12 months of “stress‑rate” repayments plus essentials. If those numbers don’t work, the loan size, structure or buffer is too aggressive.

Stress-testing a large Eastern Suburbs mortgage means modelling combined rate and income shocks, not just relying on bank approval.

Step 1: Know your real risk thresholds

For high-priced Eastern Suburbs homes, a practical ceiling for total home and investment loan repayments is around 30–35% of net household income. Above that, stress risk rises sharply, even on high incomes.

Roy Morgan’s mortgage stress work backs this up: households are ‘At Risk’ when repayments eat 25–45% of after‑tax income, depending on spending patterns, and ‘Extremely At Risk’ once they push higher on that range.

Quick rule for large loans ($2–5m):

• Aim: repayments ≤30–35% of after‑tax income at today’s rate.
• Stress-test: repayments ≤40% of after‑tax income at stress rate (today +3%).
• Buffers: 6–12 months of repayments at stress rate, plus 3–6 months essential living costs.

If you’re already near 35% at today’s rate, you’re effectively living at the bank’s APRA buffer, with little room for shocks.

Step 2: Run a simple rate-rise stress test

APRA expects lenders to test at least 3 percentage points above the actual rate. You should mirror that in your own modelling, not just rely on the bank’s tick.

Worked example: $3m Eastern Suburbs mortgage

Assume:

• Loan: $3,000,000
• Current rate: 5.8% p.a. variable (illustrative only)
• Term: 25 years, principal & interest
• Net household income: $35,000 per month

Approximate repayments:

• At 5.8%: about $19,000/month
• At 8.8% (5.8% + 3%): about $24,600/month

Impact:

• Today: $19,000 ÷ $35,000 ≈ 54% of net income.
• At stress rate: $24,600 ÷ $35,000 ≈ 70% of net income.

That’s uncomfortably above the 30–35% guide and well into Roy Morgan’s ‘At Risk’ territory.

Even if your income is higher, say $55,000 net per month:

• Today: $19,000 ÷ $55,000 ≈ 35% (top of safe band).
• Stress rate: $24,600 ÷ $55,000 ≈ 45% (stressful but potentially manageable with buffers).

Use your real rate and income, but the logic is the same: if a 3% rise pushes you above ~40% of net income, your risk climbs fast.