The Five Fama-French Factors Explained

The Fama-French Five-Factor Model includes five distinct factors that together explain a substantial portion of stock return variation. Understanding each factor is essential for interpreting factor-based analysis and constructing factor-tilted portfolios.

1. Market Factor (Mkt-RF)

The market factor, also known as the equity risk premium, measures the excess return of the broad stock market over the risk-free rate. This factor captures the fundamental compensation investors receive for bearing systematic market risk.

Mkt-RF = Return of Market Portfolio - Risk-Free Rate

Historically, the U.S. equity market has delivered an average premium of approximately 5-7% annually over Treasury bills, though this premium varies substantially over time and can be negative over extended periods.

2. Size Factor (SMB - Small Minus Big)

The size factor captures the historical tendency of small-capitalization stocks to outperform large-capitalization stocks. SMB is calculated as the average return of portfolios of small stocks minus the average return of portfolios of large stocks.

SMB = Average Return of Small Stock Portfolios - Average Return of Big Stock Portfolios

Important Note: The size premium has been weaker in recent decades compared to its historical average, leading some researchers to question whether it still exists or has been arbitraged away.

3. Value Factor (HML - High Minus Low)

The value factor captures the premium associated with "value" stocks, those with high book-to-market ratios, relative to "growth" stocks with low book-to-market ratios. HML represents the return spread between value and growth portfolios.

HML = Average Return of High B/M Portfolios - Average Return of Low B/M Portfolios

Value investing has a long intellectual tradition, dating back to Benjamin Graham and David Dodd's seminal 1934 work "Security Analysis." The Fama-French research provided systematic evidence that value stocks have historically outperformed growth stocks.

4. Profitability Factor (RMW - Robust Minus Weak)

Added in the 2015 five-factor model, RMW captures the return difference between companies with robust (high) operating profitability and those with weak (low) profitability. This factor reflects the intuition that more profitable companies should command higher returns.

RMW = Average Return of High Profitability Stocks - Average Return of Low Profitability Stocks

Operating profitability is typically measured as revenues minus cost of goods sold, interest expense, and selling, general, and administrative expenses, divided by book equity.

5. Investment Factor (CMA - Conservative Minus Aggressive)

The investment factor captures the tendency of companies that invest conservatively to outperform companies that invest aggressively. CMA measures the return spread between firms with low and high asset growth.

CMA = Average Return of Low Investment Stocks - Average Return of High Investment Stocks

This factor is related to the "asset growth anomaly" documented in academic literature, where companies expanding their asset base rapidly tend to subsequently underperform.

The factor definitions follow Fama and French's methodology using NYSE breakpoints for size and independent 2x3 sorts on size and book-to-market, profitability, or investment.