Why a weak Japanese yen could trigger intervention

The Japanese yen’s renewed weakness is testing the patience of policymakers in Tokyo and unnerving investors.

The currency fell to 154.79 against the dollar on November 12, its lowest level in around nine months, following recent declines largely prompted by the emergence of Sanae Takaichi as Japan’s new leader. Takaichi’s focus on boosting economic growth has fuelled expectations she will be reluctant to prod the Bank of Japan to raise interest rates — a move that would support the yen.

If the central bank waits longer to increase borrowing costs, the government may be forced to wade into currency markets to prop up the yen. Officials have indicated they are keeping a close eye on currency market movements, a typical first step before direct intervention.

While Japan is committed to international pacts that stipulate markets should determine exchange rates, the Group of 20 has acknowledged that excessive or disorderly currency moves can threaten economic and financial stability, giving members wiggle room to intervene when volatility spikes. Japanese officials insist it is sharp or disorderly movements — not any specific exchange-rate threshold — that trigger intervention.

The question now is how far — or how quickly — the yen needs to fall before Tokyo steps in to protect it.

Why is the yen’s weakness cause for concern?

While the yen’s slide over the past decade or so has transformed Japan into an affordable travel destination for millions of foreign tourists and boosted the profits of the nation’s biggest exporters, its weakness has become acute.

For an economy heavily dependent on imported energy and raw materials, the feeble yen drives up costs, fuelling inflation for households and squeezing margins for domestically focused businesses. The resulting cost-of-living crunch has already helped bring down two prime ministers.

There’s another reason why Japan’s government may want to act. President Donald Trump has repeatedly criticised Japan for its weak currency, arguing it gives Japanese manufacturers an unfair trade advantage. That’s a point that came up in trade negotiations between the two nations.

What is currency intervention?

When a country’s central bank steps into the foreign exchange market with the intention of strengthening or weakening its currency, that’s known as direct intervention.

In Japan’s case, the Finance Ministry decides when to act and the BOJ carries out the operation via a limited number of commercial banks. Japan will either buy yen or sell dollars to strengthen the local currency or sell yen and buy dollars to weaken it. The scale of the transactions depends on how much impact the ministry seeks and how quickly the market reacts.

Where does the money come from?

When Japan intervenes to prop up the yen, the dollars typically come from its foreign reserves in the form of cash or US Treasury holdings. As of the end of October, Japan had $1.15tn in foreign currency. During last year’s interventions, for example, Japan appeared to sell some US Treasuries from its reserves to help finance the action.

How effective is currency intervention?

Intervention is a clear way for the government to tell speculators it won’t allow its currency to go into free fall or rocket up. However, it only offers a temporary fix unless economic fundamentals driving the trend are also addressed. In addition, foreign reserves are generally there to protect the economy in the event of a major financial shock or unexpected event, not to artificially prop up the currency. A unilateral move is still seen as unlikely to turn the tide of currency momentum, but it can buy time until market dynamics change.

How often does Japan intervene in its currency market?

Japan has exchanged vast amounts of money over the years — usually to weaken the yen. But recent intervention has been in the opposite direction. The government spent a total of almost $100bn on yen-buying to prop up the currency in 2024. On each of the four occasions the exchange rate was around 160 yen per dollar, setting that level as a rough marker for where action might take place again.

To keep traders guessing, officials often don’t immediately confirm an intervention. But the ministry discloses the amount spent on intervention at the end of each month. Generating doubt and fear of losses in the market is part of the ministry’s strategy, making the comments of officials highly potent.

What is verbal intervention?

To keep traders on guard and slow movements in markets, senior officials can make remarks that hint at the prospect of intervention and bloody noses for market players. Comments by the finance minister or the ministry’s top currency official can quickly scare speculators. Officials typically use a carefully calibrated set of expressions to ratchet up their warnings and show how close they are to moving. References to “taking action” suggest intervention is close.

What are the flow-on effects of monetary intervention?

When Japan’s authorities intervene in currency markets, the immediate impact is typically sharp. Past episodes show the yen jumping around 2 yen against the dollar within seconds and 4 to 5 yen within hours.

These abrupt swings can cause huge losses for traders making speculative bets that the currency will keep moving in the previous direction. Sharp moves can also cause headaches for businesses trying to price goods, make payments and hedge against exchange rate fluctuations.

For the government, intervention also carries political and diplomatic risks. It can draw criticism for currency manipulation, especially when intervention is aimed at weakening the yen, a direction that can help exporters with trade. That charge is harder to argue when Tokyo acts to support the yen.

What is the US stance on a weak yen?

Trump accused Japan’s leaders of guiding the yen lower to gain a competitive advantage in early March and said tariffs were the solution. Japan remains on the US Treasury Department’s “monitoring list” for foreign-exchange practices after posting trade and current account surplus against US, but doesn’t fulfil all the conditions to be characterised as a currency manipulator.

Tokyo and Washington issued a joint statement in September, in which the two finance chiefs reaffirmed that intervention “should be reserved for dealing with excess volatility or disorderly movements” and not for competitive advantage. Still, Treasury Secretary Scott Bessent on October 7 said Japan’s government needed to give the central bank space to manage volatility — comments seen as a warning against excessive weakness in the yen.

Any intervention would take place after prior notice to the US and if it ended up strengthening the yen, it may be tacitly welcomed by the Trump administration.