This is Anna Crichton's final illustration for these pages.

Fingers crossed, but it looks as if deposit interest rates have found a floor.

The measure the Reserve Bank tracks - a weighted average of rates for six-month term deposits - in September was the highest it has been since February.

Trouble is, apart from those six months, the mid-1960s was the last time deposit interest rates were as low as they are now.

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And when adjusted for tax and (admittedly low) expected inflation, the real net return to depositors is barely more than 1 per cent.

That helps explain why deposits grew by just 1.1 per cent in the September quarter, the weakest growth for two-and-a-half years, and less than half the 2.4 per cent pace at which household mortgage debt rose in the same period.

It helps explain the popularity of investing in residential rental properties, to an extent that has the Reserve Bank yanking the reins.

It helps explain why 29c in the dollar of banks' debt funding comes from non-residents and why the country's net external debt is equivalent to 56 per cent of gross domestic product.

And it helps explain why a growing proportion of people 65 or older - nearly one in four -are still working.

Lousy deposit rates are not the entire explanation for any of those things, of course. But they don't help.

We may have seen the worst of that, however.

Barring a shock, as ever, next week's cut in the official cash rate to 1.75 per cent is likely to be the last for this cycle. And the banks have been warning us not to expect that cut to flow through to lower retail interest rates.

The cut has been well flagged and is therefore already baked into the wholesale interest rates that mortgages are priced off.

Moreover, banks have to take account of the funding side of their balance sheets. If the inflow of deposits slows to a meagre and exiguous trickle, they have to substitute imported savings.

Then factors like the need to lay off exchange rate risk, the broader risk premium investors demand for lending to a small and heavily indebted country, and regulatory constraints on banks' reliance on short-term offshore funding, introduced after the global financial crisis, all come into play.

It was notable that after the August OCR cut, ANZ passed on to its floating mortgage rate only five of the 25 basis points the Reserve Bank had cut by. It raised deposit rates.

Last week Bank of New Zealand chief executive Anthony Healy warned against expecting next week's OCR cut to be passed on, saying the bank was facing margin pressure as overseas wholesale funding costs rose while deposit growth cooled.

If Americans lose their minds and elect Donald Trump next week, the market reaction could be dramatic.

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ANZ chief economist Cameron Bagrie no longer sees any further OCR cuts after next week's, which he says is already effectively factored into current mortgage rates.
Banks are now rationing credit and leaning against activity at the top of the cycle, Bagrie says, and more than the regulator requires.

It is common sense, he says: excessive credit can be a key driver of booms and busts.

In the year ended September, household mortgage debt rose 9.2 per cent, more than can be explained by the combined effect of population and income growth.

More than half of an average disposable income is required to buy the median house in Auckland with a 20 per cent deposit, Bagrie says. "Despite historically low interest rates, that is on a par with 2007."

The economy's vital signs do not suggest a crying need for more monetary stimulus.

Wednesday's labour market reports, taken at face value, made cheerful reading. Employment was up strongly, outpacing brisk migration-driven growth in the labour force, so that unemployment and underutilisation rates both fell.

This week's dairy auction was encouraging and occurs against a backdrop in which the overall terms of trade were already more favourable than they have been for all but three of the past 60 years.

The Government's fiscal problem is what to do with a larger than expected surplus.

The fact that New Zealand interest rates tend to be higher than in some other advanced countries reflects New Zealanders' tendency to invest more than we save.

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This is not to say that New Zealand retail interest rates have reached some incompressible low.

There is always the risk of a shock, requiring a monetary policy response to bolster confidence.

For instance, if the Americans lose their minds and elect Donald Trump next week, the market reaction could be dramatic, as investors start to price in the risk of a trade war between the world's two largest national economies.

To say nothing of the geopolitical risks: nice little Nato you've got there. Shame if something happened to it.

Putting that gruesome possibility aside for the moment, if the next big move in interest rates is up, that does not mean it will be soon or swift.

The strength of the exchange rate counts against it, as does the persistent weakness of inflation expectations, retarding the return to 2 per cent inflation, the mid-point of the central bank's target band.

Another, more structural factor limiting the potential upside for rates is the extent of the drop in the neutral interest rate - the rate that neither stimulates nor restrains growth in economic output.

As a people we are not particularly provident, and persistently save less than is needed to find the economy's investment requirements - as evident in the chronic current account deficit.

"The fact that New Zealand interest rates tend to be higher than in some other advanced countries reflects New Zealanders' tendency to invest more than we save," Reserve Bank assistant governor John McDermott observed, in a speech reflecting on neutral interest rates two years ago.

The bank had concluded the neutral rate had fallen - to around a nominal 4.5 per cent, give or take half a percentage point - he said.

And not for a good reason, either, but largely because of weaker productivity growth, which lowers returns to investment. "If the desire to invest falls and the desire to save remains unchanged, a lower neutral interest rate will be required to reconcile savings and investment plans."