The market is pricing in an 84% probability of a rate hike by the Bank of Japan in September.
Participants on the decentralized prediction platform Polymarket have sharply revised their 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 rapid shift in market sentiment is a direct consequence of the fading effect of currency interventions by Japanese authorities. The yen, which had previously shown steady strength, is now losing ground and posting its worst weekly performance in three months.
The intervention effect is wearing off
This week, the yen has fallen by approximately 1%, reaching 159.43 against the U.S. dollar. This is the worst weekly result since May. Notably, the currency has already given back about half of the gains that followed the coordinated currency intervention by the Bank of Japan in late July and early August. Before those measures, the exchange rate held around 164 yen per dollar.
It is important to understand that this dynamic is not unique. After the April intervention, the yen returned to its 40-year lows in the following months. This suggests that one-off, targeted interventions without changes to fundamental policy cannot provide sustainable support for the national currency.
Also telling is the view of Tokyo's former top currency diplomat, Mitsuhiro Furusawa, who notes that authorities are ready to deploy currency reserves at any moment. However, he also emphasizes that officials could signal a faster rate hike to the market specifically to support the yen.
The market bets on the central bank's resolve
It is precisely this link between interventions and key rate decisions that explains the shift in expectations. Traders on Polymarket now estimate the probability of a quarter-point rate hike at above 80%. This consensus is forming as inflation approaches the target level, giving the regulator formal grounds for tightening policy.
Strategists at major banks, including OCBC, also agree that interventions alone will not reverse the yen's trajectory. The yen needs clear support from the Bank of Japan, which is ready to tighten monetary policy. Without this, any one-off measures will remain only a temporary fix.
The opposite scenario carries significant risks. If the regulator leaves the rate unchanged, the market will quickly react with disappointment—the yen has already shown declines to 160 per dollar following such decisions. Currently, market participants are betting on the central bank's actions rather than on new currency interventions.
My view: the sharp jump in probability on Polymarket is not just a speculative move, but a reflection of a real shift in the Bank of Japan's communication strategy. The regulator appears to have realized that targeted interventions without changes to interest rate policy are fighting symptoms rather than the cause. If the September hike materializes, it will signal the start of a full-fledged tightening cycle, which will have a significant impact not only on the USD/JPY pair but also on global capital flows, including cryptocurrency markets.