A bull market is formally defined as a 20% or more increase from a recent low in a broad market index, sustained over a period of time. The term contrasts with a bear market (20%+ decline) and is the market condition most investors intuitively prefer — rising prices, growing portfolios, and positive headlines. The phrase is often attributed to the way a bull attacks: thrusting its horns upward. Bull markets are the dominant state of equity markets over long time horizons, which is the mathematical foundation for the case for long-term stock investing.
Historically, bull markets have been far more common and prolonged than bear markets. Since 1928, the average bull market has lasted approximately 2.7 years and produced average gains of 112%. In contrast, the average bear market lasts 9.6 months and produces average declines of 36%. This asymmetry — more time spent rising, with larger cumulative gains — is why patient investors who stay invested through full market cycles have historically been rewarded. The longest bull market on record ran from March 2009 to February 2020 (131 months), during which the S&P 500 rose over 400%.
Bull markets are typically driven by a convergence of economic tailwinds: strong GDP growth, rising corporate earnings, low or falling unemployment, benign inflation, and expansionary monetary policy (low interest rates that reduce borrowing costs and make equities relatively attractive vs. bonds). The 2009–2020 bull market was powered by near-zero interest rates from the Federal Reserve, massive quantitative easing, a technology sector revolution, and aggressive corporate share buybacks. The 2020–2021 bull market (the fastest recovery in history) was fueled by unprecedented fiscal and monetary stimulus flooding the economy after COVID lockdowns.
Bull markets are psychologically seductive — and dangerous. As prices rise and portfolios grow, investors feel wealthier and more confident. Recency bias leads them to extrapolate recent returns indefinitely. FOMO (Fear of Missing Out) causes even conservative investors to pile into hot assets near cycle peaks: dot-com stocks at 100x earnings in 1999–2000, subprime real estate in 2005–2007, cryptocurrencies and meme stocks in 2021. Each speculative episode within a bull market ultimately ended with severe losses for late-arriving investors. The investor who bought the Nasdaq at its March 2000 peak didn't break even (in nominal terms) until 2015 — a 15-year wait.
Valuation metrics are the primary tool for assessing bull market maturity and risk. The Shiller CAPE ratio (cyclically adjusted price-to-earnings) measures stock prices relative to 10-year average earnings — a high CAPE signals stretched valuations historically associated with lower future returns. At the peak of the dot-com bull market, the CAPE reached 44; a figure above 30 has historically suggested elevated risk of a subsequent bear market, though it provides no timing precision. Other indicators — IPO volume, margin debt, retail investor participation — serve as secondary sentiment signals.
The optimal strategy during a bull market is the same as during any other market condition: maintain your target asset allocation, continue regular contributions, and rebalance when drift exceeds thresholds. Chasing bull market returns by increasing equity concentration creates timing risk — if the market turns, you now own more of a falling asset than your risk tolerance can sustain, tempting panic selling at the bottom. The investor who stayed at 70/30 stocks/bonds throughout the full 2009–2022 cycle — through the bull market, the COVID crash, the recovery, and the 2022 bear — achieved far better outcomes than those who tried to reduce bonds in the bull market and then desperately rebalanced too late.