The yen carry trade, explained: why a currency move hits US stocks and Treasuries

Most people hear that the yen is moving and tune out. That is a mistake. The yen is one of the world's primary funding currencies, and when it moves sharply the effects land on US stocks, Treasury yields, commodities and the cost of leverage itself.

Here is the plain version, without the jargon, and with the parts that are commonly stated wrong corrected.

What a funding currency is

Japan held interest rates near zero for a very long time. That made yen the cheapest money in the world to borrow, and it produced a durable trade: borrow yen at almost no cost, convert it into dollars or another currency, and buy something that yields more. US equities, Treasuries, emerging-market debt, credit. This is the yen carry trade.

The trade has two legs, and both matter. You are short yen (you owe yen you have to pay back) and long whatever you bought with it. That works beautifully while the yen is flat or weakening, because your debt shrinks in your own currency terms while your assets rise.

It works badly in reverse. If the yen strengthens, your borrowing suddenly costs more to repay at exactly the moment the position is under pressure. The standard response is to close the trade: sell the assets, buy yen, repay the loan. That buying pushes the yen higher still, which squeezes the next borrower.

That feedback loop is what an unwind is, and it is why yen moves can be violent rather than gradual.

Why the size matters

One claim gets repeated so often it is worth correcting directly, because it is now out of date: Japan is not the world's largest creditor nation. It held that position for 34 years and lost it to Germany in 2024, then fell behind China in 2025.

Japan's net external assets are still at a record high in absolute terms. It simply grew more slowly than Germany and China did. So the correct statement is that Japan remains one of the largest creditor nations on earth, third by this measure, with roughly ¥561.8 trillion in net external assets.

The claim that is still true, and is the one that matters most for US markets: Japan is the single largest foreign holder of US Treasuries, at roughly $1.2 trillion, about 13% of all foreign-held US government debt. When Japanese institutions change their appetite for Treasuries, the US government's cost of borrowing is directly affected.

What large-scale yen buying does

When yen is being bought at scale and dollar assets sold to fund it, several things tend to follow.

• A stronger yen, weaker dollar. This helps US exporters at the margin and raises the cost of imported goods over time.
• Pressure on US risk assets. Equities and credit that were supported by cheap yen-funded leverage can sell off as that funding is repaid. Growth and technology names have historically been most exposed, because they were the highest-multiple destination for that money.
• Higher US yields. If Japanese investors slow their Treasury purchases or sell outright, the Treasury has to attract other buyers, and price is how it does that.
• Pressure on Japanese exporters. A stronger yen makes Toyota, Sony and their peers less competitive abroad, which shows up in their earnings and in the supply chains attached to them.
• Policy response risk. Large, disorderly moves in USD/JPY tend to draw Japanese authorities into the market. Intervention then becomes its own source of volatility, separate from the original move.

This is not hypothetical

The mechanism above is already running. Japanese investors sold a net $29.6 billion of US government, agency and municipal bonds in the first quarter of 2026, the largest quarterly reduction in nearly four years. The driver is domestic: as the Bank of Japan has adjusted policy and Japanese yields have risen, a Japanese institution can increasingly earn an acceptable return at home without taking currency risk abroad.

That is the structural version of the same story. The carry trade was never charity. It existed because Japanese yields were unattractive. As that stops being true, the reason to send the money overseas weakens, and some of it comes home.

The bottom line

The yen is treated as a distant, technical story and it is neither. It is one of the funding currencies of the global financial system, and a meaningful share of the money that bid up assets over the past decade was borrowed in it.

When that flow reverses, capital leaves the places it was supporting, and the effect shows up in the price of nearly everything that trades: equities, bonds, oil, and the dollar itself. You do not need to trade currencies to care about the direction of the yen. You only need to hold anything that was bought with it.

Educational, not financial advice. Figures cited are point-in-time and sourced above.