Stocks fall as Iran war, 4.8% bond yields hit September

US stocks fell at the start of September as fresh strikes on Iranian targets and Treasury yields at 4.80 percent triggered a broad selloff.

"You're dealing with a global sell-off which goes back to this kind of global stimulus that we had during COVID," Robin Brooks, a senior fellow at the Brookings Institute, said. "The chickens for that are now coming home to roost."

The 10-year Treasury yield reached 4.80 percent on Tuesday, the highest since early 2025, while the 5-year touched 4.55 percent, its strongest since October 2025, according to AP data. The moves rippled across Europe, where 10-year German bunds climbed to 3.35 percent, the highest in more than 15 years, and UK gilts reached 5.14 percent, approaching levels not seen since the 2008-2009 financial crisis. Deutsche Bank analysts said the pressure was broad-based across the US, Europe and Asia, with investors rotating into defensive utilities and consumer staples while technology and real estate suffered the largest sell-offs.

The combination is testing market resilience at a historically fragile moment — September is the weakest month for stocks — and rising yields threaten to push up borrowing costs for consumers and businesses. The Congressional Budget Office estimates the federal deficit will top $2 trillion this year, about 6 percent of the economy, with total government debt at $40 trillion.

Yields at 4.80% Reshape the Risk Calculus

The bond market's move is the more consequential of the two forces because it directly reprices every future cash flow. When yields rise, the present value of corporate earnings falls, making stocks less attractive relative to safe fixed-income assets. Fed Chair Kevin Warsh said last Friday the central bank may still lift its short-term rate in coming months if inflation stays stubbornly elevated, while Treasury Secretary Scott Bessent last month announced an unusual intervention to restrain rising yields. Euro-zone inflation jumped to 3.3 percent in August, the highest in three years, adding pressure on the European Central Bank to hike when it meets next week.

Iran Strikes and the September Curse

Fresh US strikes on Iranian targets pushed oil prices higher and renewed inflation worries, compounding the yield-driven pressure. The move coincided with the start of September, historically the weakest month for equities, a seasonal pattern traders call the "September Blues." Deutsche Bank noted the defensive rotation into utilities and consumer staples is a classic reaction to the environment, with interest-rate-sensitive sectors bearing the brunt. The dollar index slipped even as the conflict escalated, a divergence traders attributed to the Fed's hawkish tilt.

Traders pointed to three converging forces for the selloff: the escalation in the Iran conflict, the jump in global bond yields, and the seasonal September weakness. Until there is clarity on either the geopolitical front or a stabilization in the bond market, equity volatility is likely to persist, with the next test coming when the ECB meets next week and the Fed's next policy decision draws closer.

This article is for informational purposes only and does not constitute investment advice.