That is trade in goods. When services such as tourism are included, Australia's share would increase by maybe four percentage points.
The goods trade in the latest year was substantially in New Zealand's favour, with exports exceeding imports by $2.4 billion, so a higher exchange rate is undoubtedly net negative.
Investment income flows are substantial too. In the latest year for which Statistics New Zealand has published figures (to March 2014) Australians earned $7.6 billion from investments in New Zealand, compared with $1.1 billion flowing the other way. A higher kiwi makes that net outflow of money look bigger to Australian eyes.
If we take a wider-angled view which includes the other 80-plus per cent of New Zealand's trade, the picture is rather different.
It is commonplace to look at nominal bilateral exchange rates, usually against the US dollar or latterly the Australian currency.
But the broader measure of currencies' competitiveness is effective or trade-weighted exchange rates, especially when adjusted for differences in inflation rates between trading partners.
The Reserve Bank's trade-weighted index fell 3 per cent in real terms in the year to February.
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The Bank for International Settlements (BIS) compiles real effective exchange rates (REERs) against a larger basket of currencies and weighted on a different basis. It recorded a decline in New Zealand's REER of just under 2 per cent over the same period.
That does not mean the kiwi is not still overvalued. Lower does not mean low.
You would be hard pressed to find a private sector economist who would quarrel with the Reserve Bank's view on March 12 that "on a trade-weighted basis, the New Zealand dollar remains unjustifiably high and unsustainable in terms of New Zealand's long-term economic fundamentals. A substantial downward correction in the real exchange rate is needed to put New Zealand's external accounts on a more sustainable footing".
Both the European Central Bank and the Bank of Japan have embarked on torrential programmes of quantitative easing (QE), while the US Federal Reserve has ceased its QE but is in no hurry to start raising interest rates.
But consider what has been happening to the big currencies over the past year.
In the year to February the US dollar rose 9 per cent relative to its trading partners, while the euro fell 10 per cent.
The Chinese renminbi appreciated 8 per cent but the Japanese yen fell 7 per cent and the Australian dollar fell 5 per cent.
They would probably all prefer a lower exchange rate but that is a mathematical impossibility.
Both the European Central Bank and the Bank of Japan have embarked on torrential programmes of quantitative easing (QE), while the US Federal Reserve has ceased its QE but is in no hurry to start raising interest rates.
Since 2010 New Zealand's REER has risen 11 per cent. Only 10 of the 61 countries the BIS monitors have seen their currencies appreciate more.
The Australian dollar has fallen 8 per cent over the same period.
The reasons for this outperformance are familiar. New Zealand has had some things going for it during the period of recovery from the global financial crisis.
The terms of trade hit the most favourable level in 40 years in the first half of last year, though they have fallen 6.4 per cent since then, giving up just over a third of their gains since the last trough in mid-2011.
Meanwhile, while we are fixated with the kiwi's ascent of Mount Parity, we are in danger of missing the epoch-making significance of China's moves to internationalise the renminbi.
The Reserve Bank was able to cut the official cash rate by 575 basis points, enough to deliver the lowest retail interest rates for 50 years, while still staying well clear of the zero lower bound which has seen some central banks resort to trillions of dollars worth of QE. It has raised the OCR since then, but the average mortgage rate, at around 6 per cent, is still only half a percentage point above the historic lows it hit in 2013.
The post-earthquake rebuilding in Canterbury is a demand pulse equivalent to a fifth of a year's GDP, providing a serious boost to construction and manufacturing.
And the low level of government debt has spared us the austerity-mongering that has hobbled recovery elsewhere.
Meanwhile, while we are fixated with the kiwi's ascent of Mount Parity, we are in danger of missing the epoch-making significance of China's moves to internationalise the renminbi.
HSBC predicts the renminbi will become fully convertible within two years and that at least half of China's trade will be settled in its currency by 2020 (22 per cent already is).
That would be a remarkable change from the situation as recently as 2013, when the renminbi was only slightly more widely traded on the foreign exchange market than the kiwi.
Beijing is moving towards an open capital account in measured steps, HSBC says.
"Policymakers ... believe larger, more volatile and two-way capital flows are the new normal for China," it says. "For an economy like China which runs a current account surplus, albeit a shrinking one, capital outflows are necessary to create a balance of payments equilibrium. This is particularly true since the People's Bank of China said it will not seek to accumulate more FX reserves." China's foreign exchange reserves at the end of last year were US$3.8 trillion.
When New Zealand abandoned a managed exchange rate and eliminated capital controls in the 1980s, the effects were profound here but insignificant for the rest of the world. When China does the same thing, the domestic effects may be just as challenging but the international ones will be seismic.
