The Rule That Drove the Japanese Yen for Decades Just Broke, Apollo Says
For years, one number told traders where the Japanese yen (JPY) was heading. That number was the gap between US and Japanese interest rates. Apollo Global Management says it no longer works.
Chief Economist Torsten Slok says the yen carry trade broke down after April 2025. Japan’s debt bill now moves the currency instead.
Why the Japanese Yen Stopped Tracking Interest Rates
The trade was simple. Investors borrowed yen at near-zero rates. They bought dollar assets paying far more. They kept the difference.
That flow tied the dollar-yen rate to the yield gap. A wider gap pushed the yen down. A narrower one pulled it back up.
Apollo’s chart tracks the two lines moving together from January 2021 until the break. Slok says the link held for decades.
Slok dates the break to Liberation Day, the April 2, 2025 rollout of sweeping US tariffs. Volatility jumped, and the trade stopped paying.
The math is unforgiving. A carry position earns a little each day. One sharp yen rally can erase a year of that. So traders cut exposure even while the gap stayed wide.
The Bank of Japan added pressure. It held its policy rate at around 1% on July 31, by an 8-1 vote. Board member Hajime Takata wanted 1.25%.
Higher Japanese yields shrink the reward for borrowing in yen. A hawkish dissent signals that reward could shrink further.
The Yield Gap Narrowed While the Yen Kept Falling
This is where the old rule falls apart.
The US 10-year Treasury yield was 4.64% on August 6, per Federal Reserve data. Japan’s 10-year bond yield was 2.76% the same day, per Ministry of Finance data.
That leaves a gap of about 1.8%. Apollo’s chart puts it near three points when the tariffs landed.
A smaller US yield advantage should mean a stronger yen. The opposite happened.
The yen sank to about 164 per dollar in late July, its weakest in four decades. It traded near 157.9 on Thursday.
Japan’s Debt Bill Now Sets the Tone
Open Japan’s budget and the new driver is hard to miss.
The fiscal 2026 budget hit a record ¥122.31 trillion ($774.5 billion). Debt servicing alone takes ¥31.28 trillion ($198.08 billion), also a record.
One line matters most. The government now assumes a long-term interest rate of 3.0%, up from 2.0% a year earlier. Tokyo is budgeting for costlier debt.
The stock behind that bill is vast. Central government debt reached ¥1,343.8 trillion ($8.51 trillion) on March 31, per Ministry of Finance data. Small yield moves cost real money.
Prime Minister Sanae Takaichi defends the plan. She says her debt-financed spending push will still deliver a primary balance surplus, the first since 1998. It also relies on ¥29.58 trillion ($187.3 billion) of fresh borrowing.
“The bottom line is that the yen carry trade has broken down, and the yen is no longer a rates story. Until volatility subsides, it will trade on Japan’s fiscal outlook rather than the interest rate gap,” Torsten Slok, Apollo Chief Economist, in the firm’s August 2 note.
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Officials have tried to defend the currency. Japan bought yen on July 30, and Washington joined a day later.
The size stays unofficial for now. Japan’s finance ministry has disclosed zero intervention through July 29. The July 30 operation falls in the next monthly report, due late August, so current figures are market estimates.
History shows how rare the US move was. The last American yen purchase came on June 17, 1998. The New York Fed bought $833 million with the dollar at ¥142.21 ($0.90). Bessent’s leaked note pointed to $5 billion to $10 billion this time.
Few expect one operation to turn the trend.
“The market’s base case appears to be that intervention may slow yen depreciation, rather than lead to lasting reversal,” Vincent Chung, portfolio manager in the fixed income division at T. Rowe Price, to Reuters.
The Bank of Japan next meets on September 17 and 18. Until then, the yen may depend less on Washington’s yields and more on Tokyo’s debt bill.
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