Here is the puzzle at the centre of the foreign exchange market.

The Federal Reserve’s target range sits at 3.50% to 3.75%. The Reserve Bank of Australia’s cash rate is 4.35%. The Bank of Japan entered its late-July meeting with a policy rate of just 1.00%.

Those numbers may look like routine central bank settings. They are not. They represent three very different economic stories, three different inflation problems and three different incentives for global capital.

During July, those gaps helped support the Australian dollar, left the Japanese yen near multi-decade lows and turned AUD/JPY into one of the clearest expressions of the global rate divide.

Quick facts

Selected currency leaderboard

Strongest mover: Australian dollar

The Australian dollar was among July’s stronger major currencies, trading from around US$0.6900 to above US$0.70 during the latter part of the month.

At first glance, the explanation appears straightforward: Australia has a 4.35% cash rate. That is higher than the policy rate in several comparable economies, and higher relative yields can make a currency more attractive.

But that is only half the story. The other half is why the RBA has kept policy so restrictive. Inflation has slowed, but underlying price pressure remains above the central bank’s target range. That leaves the RBA with less flexibility than markets might otherwise expect.

The 11 August meeting is therefore not simply another rate decision: it is a test of whether the RBA believes the inflation problem is genuinely receding, or merely changing shape.

Risks and constraints

The Australian dollar’s yield advantage matters, but it does not operate in isolation.

China’s economy expanded by 4.3% over the year to the June quarter. That sounds resilient until the components are examined: industrial production rose by 5.3% over the year in June, retail sales increased by only 1.0%, and fixed-asset investment declined by 5.7% during the first half.

That gap matters because Australia is not equally exposed to every part of China’s economy. Strong factory production may support demand for some raw materials, whereas weak household consumption and property investment may point in the opposite direction.

So the Australian dollar enters August with two competing forces: Australia’s interest-rate settings are supportive, while China’s uneven recovery is not. A softer RBA assessment could reduce the currency’s rate advantage, and continued weakness in Chinese construction or commodity demand could add another constraint. Persistent Australian inflation, however, may keep restrictive policy expectations alive.

Weakest mover: Japanese yen

The yen remained under broad pressure during July, with USD/JPY trading near the 162.53 to 163.00 region. That level is remarkable, but the mechanism behind it is even more important.

The Bank of Japan raised its policy rate to 1.00% on 16 June. In another era, a Japanese rate increase might have been expected to support the yen; instead, the currency remained weak.

Why? Because foreign exchange markets do not compare a country’s current interest rate with its own past: they compare it with the rates available everywhere else. Japan’s 1.00% policy rate remains far below Australia’s 4.35% cash rate and the Federal Reserve’s 3.50% to 3.75% target range.

That gap continues to create an incentive for carry activity, where investors borrow in a lower-yielding currency and allocate capital towards higher-yielding markets.

Risks and constraints

The yen’s weakness may appear entrenched, but that does not make it permanent. Currency markets can change direction rapidly when heavily held positions begin to unwind.

A more restrictive signal from the Bank of Japan could force markets to reassess the expected pace of policy normalisation. Similarly, a decline in US yields could narrow Japan’s relative disadvantage, and a broader risk-off move could encourage investors to close yen-funded positions, potentially creating a sharp counter-move in the currency.

Official commentary is another factor: if yen weakness becomes rapid or disorderly, markets may become increasingly sensitive to statements from Japan’s Ministry of Finance. The lesson is simple: a weak currency can remain weak for a long time, until the assumptions supporting that weakness begin to change.

Most important cross: AUD/JPY

If there is one currency pair that captures the Asia-Pacific policy divide, it may be AUD/JPY.

On one side is Australia, with a 4.35% cash rate, commodity exposure and an inflation problem that may keep policy restrictive. On the other is Japan, with a 1.00% policy rate, heavy reliance on imported energy and a central bank moving cautiously towards normalisation.

The policy-rate difference is 3.35 percentage points. That is not a footnote: it is the central mechanism behind the cross.

What could shift the outlook?

The current logic supporting AUD/JPY is clear: Australia has the higher rate, Japan has the lower rate, and carry demand favours the Australian side of the cross. But markets rarely break because the obvious story becomes more obvious: they break when the obvious story stops working.

AUD/JPY may remain supported if the RBA maintains a restrictive stance and the Bank of Japan continues to move gradually. That support could weaken if Australian inflation falls faster than expected, the RBA adopts a less restrictive tone or Chinese commodity demand deteriorates.

A more hawkish Bank of Japan signal could support the yen, while falling US yields or a broader risk-off move could also trigger the unwinding of carry positions. The crucial question is not simply which central bank has the higher rate today, but which central bank may surprise markets tomorrow.