The market is pricing in an 84% probability of a rate hike by the Bank of Japan in September.
Analyzing the latest data from the decentralized forecasting platform Polymarket, I note a sharp shift in market participants' expectations regarding Japan's monetary policy. In just two weeks, the probability of the Bank of Japan raising its key interest rate at the September meeting has surged from 22% to 84%. This is one of the fastest consensus revisions I have observed in recent months.
The key trigger for this reversal was the weakening effect of currency interventions by Japanese authorities. The yen, which had previously shown confident strengthening, is now losing ground. Over the past week, the USD/JPY exchange rate rose by approximately 1%, reaching 159.43. This is the worst weekly performance for the Japanese currency since May of this year.
It is particularly telling that the yen has already given back about half of the gains it made following the coordinated currency intervention in late July and early August. At that time, the exchange rate pulled back from around 164 per dollar. We now see that one-off measures without changes to fundamental policy parameters cannot provide sustainable support for the national currency.
A similar scenario has already unfolded before: after the April intervention, the yen slid back to its multi-year lows in the following months. This confirms my long-standing position: targeted interventions without monetary policy tightening are merely a temporary measure.
Notably, Tokyo's former top currency diplomat Mitsuhiro Furusawa recently commented that the possibility of reusing currency reserves cannot be ruled out. However, according to him, authorities are also prepared to signal a faster rate hike to support the currency. It is precisely this signal that traders now appear to be pricing into their models.
OCBC strategists agree that interventions alone are insufficient to reverse the yen's dynamics. The market needs clear and unambiguous support from the Bank of Japan, which is ready to tighten policy. Given that inflation is approaching the target level, the case for such a move is becoming increasingly compelling.
However, the opposite scenario also carries risks. If the regulator leaves rates unchanged, the market reaction will be immediate and painful—the yen could quickly fall to 160 per dollar. Market participants are currently betting on a central bank move, not on new interventions.
My analysis: The market appears to have shifted from a "currency defense" mode to a "monetary tightening expectations" mode. The 84% probability looks overstated, but the trend itself is obvious. The Bank of Japan will have to choose between the risk of disappointing the market and the risk of losing control over inflation and the exchange rate. Under current conditions, hesitation will cost more.