Early Signs of a Property Downturn — What the Data Shows Before Prices Fall

Days on market (DOM) is the clearest early indicator of a market cooling. In a genuine boom, properties sell in under three weeks. Buyers compete, sellers hold leverage, DOM compresses. When that urgency fades, DOM starts to drift.

The threshold matters. Our detection formula uses 45 days as a hard cutoff — any suburb sitting above it cannot qualify as booming, regardless of how strong its growth rate looks. Forty-five days is not arbitrary: it marks the shift from a market where demand clearly outstrips supply to one where buyers have time to think, negotiate, and walk away.

What makes DOM valuable is how early it moves. Annual growth figures are lagging — they reflect what happened over the past twelve months. DOM responds to this month’s buyer behaviour. A suburb can still report strong annual growth while DOM is already climbing, because the annual figure includes the hot months from six or nine months ago. If DOM crosses 45 while the annual growth number is still positive, you may be looking at a suburb that has already turned.

Rental vacancy is the supply-and-demand ratio for the rental market. When vacancy is very low — below 1.5% — landlords hold the pricing power. Every time a tenant leaves, there’s a queue of replacements. Rents hold or rise. Investors compete to buy into the suburb.

Once vacancy climbs past 2%, that dynamic reverses. Landlords start offering incentives. Rents soften. The flow of investor buying interest that sustained price growth begins to thin. The hard filter in our formula is vacancy at or below 2% — a suburb above that threshold cannot produce a boom signal regardless of what its growth rate or days on market shows.

What makes vacancy particularly useful as a warning signal is the direction of travel. A suburb that was sitting at 1.2% vacancy twelve months ago and is now at 2.5% is telling you something that the trailing annual growth figure hasn’t caught up to yet. The rental market is faster-moving than the sales market — supply imbalances show up in vacancy months before they show up in sold prices.

SQM Research publishes free postcode-level vacancy data with 16 years of monthly history. It’s one of the most useful free tools available to Australian investors — and one of the most underused. Watching the vacancy trend for a suburb you own or are considering over 6–12 months tells you far more than any single snapshot.

This is the strongest and most reliable of the three signals. In our 78-suburb backtest, every single suburb that boomed was priced well below its capital city median at the start of the boom. Suburbs priced above 1.5 times the city median consistently underperformed.

The mechanism is straightforward. Buyers who are priced out of premium suburbs move down the price curve into the next affordable tier. That demand displacement drives growth in suburbs below the median. Once a suburb has already run hard and closed that affordability gap — or exceeded the city median — it has absorbed most of that inbound demand. The buyers who would have arrived there have already arrived. The next wave starts looking further out.

Affordability headroom is also a measure of remaining upside. When less than 30% of the gap between a suburb’s median and the city median has been closed, detection still catches the suburb in the early phase of a boom — typically with 60–85% of the total gains still ahead. Once more than 70% of that gap has been consumed, the suburb has run most of its race.

This is the only cross-suburb ranking signal that survived tide cancellation in our backtest. When you remove the market-wide rising tide — the fact that all suburbs tend to grow during boom periods — affordability relative to the city median is the signal that consistently explains which suburbs outperform their peers.

There’s a fourth pattern worth understanding alongside the three warning signs: mean reversion. Past outperformers tend to underperform going forward.

This runs counter to how most investors instinctively think about property. The instinct is to find the suburb that has been growing strongly and buy in before it becomes too expensive. But the data doesn’t support that approach. A suburb that has already run hard has, almost by definition, consumed its affordability headroom. The buyers who drove the boom have already arrived. The demand displacement has already played out.

What’s left is a suburb that now sits closer to the city median — or above it — with slower DOM, potentially rising vacancy, and investors rotating into the next opportunity. The trailing growth number still looks good. The forward picture is much less compelling.

Boom size is era-dependent — the pre-2015 median boom produced 1.3% outperformance, while the post-2020 median was 16.2% — but the mean reversion pattern holds across both periods. The question is always: how much of the run is still ahead?

The walk-forward backtest across 12,360 postcode-months produced four tiers. The spread between best and worst is 13.9 percentage points of excess return — and it’s perfectly monotonic. There is no tier reversal, no noise in the ordering.

Walk-forward backtest, 12,360 postcode-months. No lookahead. Excess return = suburb 12-month growth minus market median growth. Full methodology →

The Pass tier is not just “low growth.” It’s active underperformance — 6.4 percentage points below the market median, with only 28% of postcode-months beating the benchmark. That means if you hold property in a Pass-tier suburb, roughly three quarters of the time the broader market is growing faster than you are.

The Watch tier is instructive too. At −0.7pp and 47% beating the market, Watch suburbs essentially track the market. You’re neither well ahead nor badly behind. The gap between Watch and Pass is 5.7 percentage points of annualised return — the cost of buying into a suburb where all three warning signs are present vs. one that’s simply cooling.

All three warning signs can be checked using public sources. No subscription required.

If you own in a suburb showing all three warning signs — DOM trending past 45, vacancy climbing above 2%, price now sitting above the city median — the data doesn’t tell you to sell. Property is not a liquid asset and transaction costs are high. But it does tell you what not to do: don’t double down. Don’t buy the adjacent property as a portfolio add-on. Don’t read the trailing annual growth figure and assume the momentum continues.

If you’re evaluating a suburb as a potential purchase, the warning signs give you a clear filter. A suburb with one sign needs deeper investigation. A suburb with all three fails the hard filters in our detection formula — it cannot score above the boom threshold regardless of what else looks attractive about it.

The asymmetry is worth stating clearly. Strong Buy suburbs returned +7.5pp excess over the market with 71% of postcode-months beating the benchmark. Pass suburbs returned −6.4pp with only 28% beating the benchmark. That 13.9pp spread doesn’t come from finding magic suburbs. It comes from avoiding the wrong ones just as much as identifying the right ones.