Japan's currency intervention is a bandage, not a cure

THE LAST TIME the United States and Japan intervened jointly in the foreign-exchange market was in 2011, after an earthquake and tsunami devastated the Tohoku coast. The two governments acted then to weaken an overstrong yen, not to prop up a collapsing one. Now they have done the reverse, marking the first coordinated dollar-selling, yen-buying operation in 15 years. The dollar, which had fallen to 163.99 yen on July 23rd, its weakest level since 1986, was pushed back to the lower 150s within days. The intervention was swift, costly and dramatic. It was also a temporary fix for a structural problem.

Japan's finance ministry has already confirmed that further joint action is possible. Ms Satsuki Katayama, the finance minister, said on Monday that Tokyo and Washington would "not hesitate" to act again, and Mr Scott Bessent, the US treasury secretary, echoed the warning. The yen briefly touched 155.20 against the dollar after the announcement, its strongest level since early May. Traders are now watching whether that psychological threshold holds. It probably won't, unless the policies driving the yen's weakness change.

The reason is not hard to see. The yen's slide is not an accident or a market glitch. It is the arithmetic consequence of policy choices made in Tokyo, compounded by a global energy shock. At its centre is an interest-rate gap that is both wide and persistent. The Bank of Japan raised its policy rate to 1% in June, the highest level since 1995. But the Federal Reserve's rate sits between 3.5% and 3.75%. That differential is the primary engine of dollar demand: investors selling yen to buy higher-yielding American assets. As long as the gap remains, the yen faces a headwind that no amount of foreign-exchange intervention can eliminate.

To be sure, central banks have intervened before. Japan alone spent ¥11.7 trillion ($72.5bn) on yen-buying in April and May, a record monthly amount, and another ¥4-5 trillion in the recent joint operation. The market estimate, based on BOJ data, puts Friday's joint spend at around $25.5-36.5bn. But earlier interventions this year produced only fleeting rebounds. The currency would recover, then slide back. What distinguishes the current episode is American participation, which has lent credibility that unilateral actions lack. Coordinated interventions since 1995 have historically had longer-lasting impact, as they prompt short-covering and signal that the market will be met with substantial, sustained counterforce. The US Treasury apparently sold euros to buy yen, using a pandemic-era Federal Reserve backstop facility for major central banks. That is a non-trivial signal.

Yet credibility is not the same as a solution. The deeper problem is fiscal. Prime Minister Sanae Takaichi, who took office in October, is a disciple of Abenomics - the programme of big fiscal spending and monetary easing deployed by her predecessor Shinzo Abe to pull Japan from prolonged deflation. Ms Takaichi's first economic blueprint, finalised in July, pledged to invest heavily in strategic industries, with combined public and private spending projected to exceed ¥370 trillion ($2.28 trillion) through fiscal 2040. Ditching language from previous administrations about restoring fiscal health, it substituted a vaguer pledge of "fiscal sustainability".

The markets did not take kindly to the message. The benchmark 10-year Japanese government bond yield climbed to 2.9% in July, its highest level in nearly three decades, as investors fled long-dated debt. Japan's debt pile already exceeds twice the size of its economy, the worst ratio among developed nations. New bond issuance in fiscal 2026 will reach ¥29.6 trillion, up 3.3% from the previous year. Debt-servicing costs - the interest the government pays on outstanding bonds - rose by more than 10% in this year's budget to ¥31.3 trillion, the first time the figure has surpassed that level. Fitch Ratings projects the fiscal deficit widening to 3.7% of GDP by fiscal 2027, up from 2.4% in fiscal 2025.

The political incentive is clear. Ms Takaichi campaigned on reversing fiscal austerity and has proposed suspending Japan's 8% food tax for two years, at a cost of roughly ¥5 trillion per year. The administration has already enacted a supplementary budget of ¥3 trillion to shield households from rising energy costs, part of the Iran conflict fallout. The primary budget forecast - which excludes new bond sales and debt servicing - has been revised from a ¥3.6 trillion surplus to a ¥800bn deficit. The arithmetic is unforgiving: more spending, more borrowing, higher yields, a weaker currency. That is not a contradiction. It is a cycle.

The Bank of Japan is caught in the middle. Governor Kazuo Ueda has signalled readiness to raise rates further, and most analysts polled by Reuters expect the policy rate to reach 1.25% by year-end. But Ms Takaichi's blueprint was widely read as discouraging the BOJ from moving faster - a draft phrase calling for monetary policy that "bolsters private demand" was eventually removed after market panic, replaced by a footnote affirming central-bank independence. Core consumer inflation, at 1.6% in June, remains below the BOJ's 2% target, giving the governor cover to move slowly. But producer prices rose 6.3% in May, the fastest pace in over three years, as energy costs feed through the supply chain.

That is where the system begins to creak. The BOJ needs to raise rates to defend the yen and contain inflation. The government needs low rates to keep its debt sustainable. Both are true. They are also incompatible. Intervention can buy time, but it cannot reconcile the contradiction. As one market strategist at the Monex Group observed, intervention without a change in domestic monetary policy is like tapping the brake while keeping your foot on the accelerator. You might slow down briefly. Eventually you will burn through your brakes.

The US involvement adds a second layer of incentive that is worth examining. Washington's participation is not purely altruistic. A destabilised yen risks spillovers: higher Japanese bond yields tend to lift American yields too, an unwelcome development ahead of congressional midterm elections in the fall. A weaker dollar also makes American exports more competitive in yen terms. Mr Trump called the intervention a "signal of friendship" that would benefit the world economy, which is not entirely wrong. But the alignment of interests is transactional as well as strategic.

So what should happen next? The first task is for Ms Takaichi's government to show that its spending ambitions can be financed without wrecking the currency or the bond market. That could mean a clearer timetable for primary surplus restoration, even if it falls years away. It could mean targeting investment more narrowly rather than casting a wide net. The blueprint's vague pledge of "fiscal sustainability" is not enough. Markets will not be reassured by language that has no arithmetic behind it.

The second task is for the BOJ to tighten at a pace the market finds credible. The current trajectory - roughly one hike every six months - has proved too slow to stem capital outflows. A faster cadence would risk growth, but the alternative is persistent imported inflation and a currency that continues to erode living standards. The cost will not fall evenly. Pensioners and low-income households are most exposed to food and energy prices. But subsidies are a blunt and expensive way to cushion them. Better to allow the BOJ to do its job and target transfer payments precisely.

155 yen to the dollar is indeed the next test. If the yen holds there, it will be because traders believe intervention has a credible backstop and policy will shift. If it breaks, the message will be equally clear: the market does not trust words over arithmetic. That is a lesson central banks have been trying to teach for decades. Japan's policymakers would do well to listen.