EXCLUSIVE: The Biggest Risk To S&P 500's Historic Run Could Be One Number: 5%

The S&P 500 has spent much of the past year defying gravity. Despite sticky inflation, shifting Federal Reserve expectations and rising Treasury yields, stocks have continued to grind higher as investors bet on artificial intelligence, resilient earnings and a still-growing economy.

But according to exclusive comments shared by WisdomTree's Kevin Flanagan, one number may matter more than any other in the months ahead: 5% — the level on 10‑year Treasury yields that could send tremors through the stock market.

The Yield Threshold Wall Street Is Watching

Treasury yields have climbed steadily in recent weeks as investors reassessed the outlook for inflation and interest rates after the energy price shock from the Iran war fueled an acceleration in consumer-price increases.

The benchmark 10-year bond yield has jumped 62 basis points from levels before the start of the Middle East conflict to 4.57%, after hitting a 16-month high of almost 4.70% earlier this week.

While markets expected multiple Federal Reserve rate cuts as recently as February, renewed inflation concerns have revived “higher-for-longer” rate fears.

That shift has pushed the 10-year yield toward a level that has historically created challenges for equities.

“The question is whether a 5% UST 10-year yield is a headwind for stocks in general,” Flanagan said. “History suggests it very well could be.”

The comment highlights a growing tension in financial markets. Stocks continue to trade near record highs, while bond markets are pricing in the possibility that interest rates may remain elevated for longer than investors previously expected.

Why 5% Matters

Treasury yields serve as the foundation for asset valuations across financial markets.

As yields rise, investors can earn more from government bonds with little credit risk, reducing the relative appeal of equities. Higher yields also increase borrowing costs for businesses and can put pressure on the valuation multiples that have helped fuel the market’s rally.

That dynamic becomes particularly important for growth-oriented sectors, where investors are willing to pay today for earnings expected years into the future.

The higher interest rates move, the less valuable those future cash flows become in present-value terms.

Stocks Vs. Bonds

For now, investors appear comfortable looking past rising yields. But Flanagan’s comments suggest the bond market may be sending a warning signal that equity investors should not ignore.

If inflation concerns persist, bond yields could remain elevated and increase pressure on stock valuations.

Investors have increasingly used fixed-income ETFs such as the iShares 20+ Year Treasury Bond ETF (NASDAQ:TLT) and the Vanguard Extended Duration Treasury ETF (NYSE:EDV) to position for eventual declines in interest rates. However, a sustained move toward or above a 5% 10-year Treasury yield could complicate that thesis and reinforce the case for higher-for-longer rates.

A Risk Market Bulls Can’t Ignore

The S&P 500’s rally has survived multiple challenges over the past two years, from recession fears to inflation shocks and shifting Fed policy expectations.

Yet Flanagan’s warning underscores a reality that equity investors have not faced consistently in more than a decade: government bonds once again offer meaningful competition for investor capital.

As long as Treasury yields remain contained, stocks may continue to shrug off macro concerns. But if the 10-year yield decisively moves through 5%, history suggests investors may be forced to pay much closer attention to what the bond market is saying.

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