The Japanese yen fell to about 164 per dollar last week. That is its weakest price since 1986. Whatever you were doing in 1986 — and some of us were doing it in parachute pants — Japan’s money has not been this cheap since.
What happened next is the remarkable part. The United States and Japan stepped in together to prop the yen up. That is the first joint rescue of the currency in a generation.
Tokyo spent tens of billions of dollars buying its own money. Washington added something genuinely new: a special loan of dollars to Japan, backed by Japan’s $1.1 trillion pile of U.S. Treasury bonds. The loan program has a $60 billion cap, and Treasury Secretary Bessent wants that cap raised.
It worked, for the moment. The yen recovered to around 156 to 157 per dollar.
Notice the clever mechanics. Japan owns more U.S. government debt than any other country on Earth. Selling those bonds to raise dollars would rattle the bond market. So instead of selling them, Japan is using them as collateral — like pawning a watch instead of selling it. Washington lends against the collateral, Tokyo buys yen with the loan, and nobody has to dump a bond. Elegant. Also a measure of how serious the moment got.
Why the yen was sinking
Japan’s problem is arithmetic, not mystery. Its government debt is about 230% of GDP — more than double the size of its entire economy. That is the heaviest debt load in the developed world.
The Bank of Japan, Japan’s version of the Federal Reserve, is still buying roughly ¥2.5 trillion of government bonds every month with newly created money. Its interest rate sits at 1%. Inflation there runs at 1.7%.
Keep your interest rate below inflation while printing money to buy your own bonds, and your currency drifts downhill. That is not exotic finance. That is a bathtub with the drain open.
Markets expect Japan’s central bank to finally start raising rates in September. Until it does, analysts quoted by the Journal are openly skeptical the rescue holds. One Journal column summed up the strangeness: “America is printing dollars so Japan can buy yen.”
The trillion-dollar tripwire
Here is why a currency 5,000 miles away matters to a retirement account in California.
The bank HSBC estimates there is more than $1 trillion in yen “carry trades” outstanding. A carry trade means borrowing money where it is cheap — Japan — and investing it where returns are higher, which is almost everywhere else.
A carry trade is a lovely business until the currency you borrowed starts rising. Then your cheap loan gets more expensive by the day, and you have to sell whatever you bought to pay it back.
We have seen the fire drill. In the summer of 2024, a sudden yen surge forced exactly that kind of unwind, and markets around the world lurched for a week. The same wiring is in place today, with more current running through it.
Follow the sequence. The rescue only truly holds if Japan raises rates. If Japan raises rates, the yen strengthens. If the yen strengthens quickly, a slice of that trillion dollars has to come home fast — and borrowed money coming home does not sell what it should. It sells what it can, including perfectly good American stocks that never heard of the yen.
None of this is a prediction. September may arrive gently. But a retirement portfolio should not need Japan’s central bank to behave gently.
That is the whole reason we watch stories like this one. Not to trade them — to make sure your portfolio never depends on them going well.