How To Manage Interest Rate Rises During a Long Off‑the‑Plan Build

If you’re partway through a long 18–36 month off‑the‑plan build, managing interest rate rises means two things: 1) stress‑testing your future repayments at least 3% above today’s rates, and 2) using the build period to build buffers, reduce bad debt and lock in a flexible loan strategy before settlement. If your budget only works at today’s rate, it’s too fragile.

Here’s how to turn a vague worry into a concrete, one‑week plan.

Use the build period to model higher-rate scenarios and adjust early.

1. Understand your real interest rate risk on a long build

Why rate risk is different for off‑the‑plan

With an off‑the‑plan purchase, your lender will fully reassess your loan at settlement using:

1. Current interest rates, not the rate when you exchanged.
2. A serviceability buffer (usually at least +3% above the actual rate, per APRA guidance).
3. The lower of the contract price or final valuation (Fact 5).

So you wear risk twice: higher rates and possibly lower valuation. That’s why you should already be stress‑testing both, not just the purchase price. [[/insights/off-the-plan-valuation-change-before-settlement]] explains the valuation side in more detail.

What recent RBA moves tell you

The RBA has taken the cash rate from pandemic lows of 0.10% back up to the mid‑4s (4.35% in May 2026) as it fights persistent inflation. Roy Morgan estimates about 28% of mortgage holders are now ‘At Risk’ of mortgage stress as rates bite.

You don’t control the RBA. You do control how fragile your numbers are.

2. Stress‑test your future repayments properly

A worked example

Assume:

• Contract price: $900,000
• Deposit at exchange: 10% ($90,000)
• Expected loan at settlement: $810,000
• Term: 30 years, principal and interest

Indicative monthly repayments:

• At 5.5%: about $4,600 per month
• At 7.5% (+2%): about $5,660 per month
• At 8.5% (+3%): about $6,240 per month

That’s a $1,600 per month difference between 5.5% and 8.5% — a level of movement we’ve seen before in Australia over a few years.

If your budget only works near 5.5%, you’re exposed.

Use at least a +3% buffer

Off‑the‑plan buyers should already be:

• Stress‑testing at least 3% above prevailing rates (Fact 8).
• Assuming lenders will assess you at that higher rate plus the buffer.

If your surplus at +3% is less than one week’s after‑tax income, or you’d be in the Roy Morgan ‘At Risk’ camp, you need to adjust something now: loan size, buffers, or timing.

For a deeper walk‑through on modelling different rate scenarios, see [[/insights/planning-rate-rises-before-off-the-plan-loan-drawdown]].