Setting a Safe Cash Buffer When Your Mortgage Is Big

Affluent borrowers with large Australian home loans should usually hold 6–12 months of stressed mortgage repayments plus essential living costs in cash or a true offset account, with 3–6 months as a hard minimum before you add new investments. The higher your loan size, income volatility or gearing, the closer you want to be to 12 months or more.

That’s the decision-grade answer. The rest of this guide shows you how to calculate your number, where to park it, and how to build it without stalling your wealth plan.

Translate your cash buffer into a clear dollar target based on stressed monthly costs.

1. What “cash buffer” should an affluent borrower aim for?

Think in months of total essentials, not just a random savings balance.

Core rule of thumb:

• Minimum: 3–6 months of stressed repayments + essential living
• Preferred for large loans: 6–12 months
• Go higher (12–18 months) if you’re self‑employed, in cyclical industries, or heavily geared across multiple properties

“Stressed” means modelling your home loan at current interest rates + 3%, in line with APRA’s typical serviceability buffer.

This lines up with existing guidance that geared households should hold at least 3–6 months of stressed costs before investing further, and 6–12 months when risk is higher or income is lumpy (/insights/how-big-should-your-cash-and-offset-buffer-be-when-youre-geared).

Quick worked example

• Loan: $2.5m, 25 years remaining
• Current rate: 6.0% p.a., stressed at 9.0%
• Stressed P&I repayment ≈ $21,000 per month
• Essential living (after trimming non‑essentials): $9,000 per month

Stressed monthly total: $30,000.

• 3‑month minimum buffer: $90,000
• 6‑month safer level: $180,000
• 12‑month resilient level: $360,000

For a $2.5m mortgage, most affluent borrowers should be targeting $180k–$360k in true cash/offset buffer.