The S&P 500 bull market reached its fourth anniversary on October 12 after gaining nearly 120% from its October 2022 closing low, according to CNBC. The milestone is substantial, but age alone does not end a market cycle. The more useful question is whether earnings can keep pace with valuations while participation broadens beyond a small group of technology leaders.
Four years of concentrated gains
Artificial intelligence spending has been the clearest driver of the latest stage of the rally. Nvidia and other suppliers of chips, memory and data-center infrastructure delivered outsized gains as investors priced in a long investment cycle. That concentration matters because technology represents about 40% of the S&P 500 in the source data. A reversal in a few large companies can therefore move the entire index even when most constituents are stable.
Official S&P Dow Jones Indices data confirms that large-cap U.S. equities remained near records in October 2026. The index provider also describes the S&P 500 as covering roughly 80% of available U.S. market capitalization. This makes the benchmark a strong measure of large-company performance, but not a complete picture of smaller businesses or equal-weight participation.
Breadth is the central warning
CNBC reported that 75% of S&P 500 stocks fell during September, while small-cap shares weakened relative to the largest companies. Market breadth measures how many stocks participate in a move. Weak breadth does not predict an immediate decline, but it makes the index more dependent on continued strength from its biggest constituents.
Oppenheimer strategist Ari Wald placed the current cycle as the sixth longest of 24 bull markets since 1932. His historical sample showed a median 13 months remaining for comparable cycles and a median fifth-year return of 21%. Those figures describe history, not a forecast. The range of outcomes around a median can be wide, and today's index concentration is unusually high.
Rates and earnings set the next test
Higher Treasury yields raise the discount rate used to value future profits, which can weigh most heavily on companies priced for rapid long-term growth. At the same time, a strong earnings season may not be enough if results merely meet elevated expectations. Companies must sustain growth without repeated guidance disappointments.
Investors should watch three signals: equal-weight versus cap-weight index performance, the Russell 2000 around its 200-day moving average, and earnings revisions for the largest technology companies. A fifth year of gains remains possible, but a healthier advance would require more companies to contribute. BTI's conclusion is that the bull market's age is less important than the combination of breadth, real earnings growth and the cost of capital.