The bull market is turning 4 years old — but yields could crash the party

This bull market has now run for four years, and technology stocks have been the dominant engine throughout. Whenever investors asked which sector would lead, tech was the answer. That leadership has shaped index returns, portfolio allocations, and the broader market narrative.

The complication is bond yields. When yields rise, they lift the discount rate applied to future corporate earnings, which tends to weigh most heavily on growth-oriented companies whose valuations rest on profits expected years ahead. Tech sits squarely in that category. Higher yields also make fixed income more competitive as an alternative to equities, potentially drawing capital away from stocks.

What to watch is the direction and pace of yield moves, not any single reading. A gradual drift higher may be absorbed; a sharp spike has historically pressured long-duration growth names. For long-term investors, the more useful question is whether earnings growth can continue to justify valuations if borrowing costs stay elevated. The bull market's age alone says little about its durability.