National Australia Bank expects Australia's September labour force report to show employment rising by 20,000 and the unemployment rate holding at 4.6%, with the bank flagging some risk of a lower jobless reading. The figures are due for release at 11.30am Sydney time on Thursday, which corresponds to 0030 GMT on Thursday and 8.30pm US Eastern time on Wednesday. The Australian Bureau of Statistics is scheduled to publish the report, its monthly household survey tracking employment, hours worked and job-seeking.

NAB's 20,000 forecast is in line with Westpac's projection and the market consensus. CBA expects a softer gain of about 10,000. Despite the differing employment estimates, all three banks see the unemployment rate unchanged at 4.6%. Spread-out calls like these are common for a series that is volatile month to month and subject to revision.

With NAB, Westpac and the consensus all at 20,000, and the three major banks seeing unemployment steady at 4.6%, the bar for a surprise sits mainly in the jobless rate itself. A drop to 4.5% would revive the case for further Reserve Bank of Australia tightening — the central bank's objectives span both low inflation and full employment — and could support the Australian dollar and short-dated yields. Conversely, a rise to 4.7% would push in the other direction, adding weight to the view that the central bank's four rate hikes are already doing enough.

A 4.6% outcome would leave the jobless rate margin above the 4.5% projection for the fourth quarter set out in the Reserve Bank of Australia's August Statement on Monetary Policy, the central bank's quarterly economic outlook. According to NAB, that gap would not, in itself, materially change the RBA's assessment of the labour market. Rather, the central bank's view would only be expected to shift if unemployment kept surprising to the higher side through to year-end.

NAB argues that much of the recent cooling in the labour market reflects more people entering the workforce rather than a weakening in hiring, and the bank sees indicators of labour demand remaining resilient. Because the jobless rate measures the share of the labour force that is out of work and actively looking, a wave of new entrants can lift it even while employers keep hiring — the arithmetic behind NAB's supply-led interpretation. That supply-led character of the cooling matters for the rates outlook as well: rising labour force participation eases wage pressure without signalling a hiring slump, which in turn gives the RBA less reason to sound alarmed about growth.

NAB said August's jump in unemployment appeared partly due to residual seasonality and partly to methodology changes. Residual seasonality refers to seasonal patterns that the adjustment process did not fully strip out. The methodology changes were made under the Australian Bureau of Statistics' Labour Force Modernisation project. Together, the two factors raise the prospect of some payback this month. In NAB's assessment, August's rise was in part a statistical quirk — though not one large enough to drag the rate back to 4.5% this month.

Despite the case for statistical payback, two factors stop NAB from making a 4.5% print its base case for September. First, the eighth of the survey sample — the rotation group leaving the panel this month — carries an unusually low unemployment rate, so its departure tends to push the measured rate higher. Second, August's rate stood at roughly 4.65% before rounding, meaning it could fall almost a full tenth of a percentage point and still be reported as 4.6%.

The outcome will feed directly into the debate over whether the RBA, having lifted the cash rate four times to 4.60%, needs to go further. On NAB's reading, a steady 4.6% print would not be enough to shift that assessment. A run of upside surprises in unemployment through to year-end, however, would be.