Definition
Alpha measures the skill component of investment returns — how much a portfolio manager or strategy adds beyond what the market compensates for risk-taking. It's calculated using the Capital Asset Pricing Model (CAPM): if a stock's expected return (given its beta) is 10% and it actually returns 13%, alpha = +3%. Generating consistent alpha is famously difficult — most active managers underperform their benchmark after fees. Hedge funds, quant strategies, and value investors historically claim to seek alpha. Alpha is time-window and benchmark-dependent, so headline numbers should always specify both. In efficient markets, alpha is a zero-sum game: for every dollar of alpha someone earns, someone else loses.
α = Rp − [Rf + β(Rm − Rf)]
Rp = actual portfolio return, Rf = risk-free rate, β = portfolio beta, Rm = market return; the bracketed term is CAPM expected return
Example
Portfolio returns 13% in a year when: risk-free = 4%, market return = 10%, portfolio beta = 1.2. Expected return per CAPM = 4 + 1.2(10 − 4) = 11.2%. Alpha = 13 − 11.2 = +1.8%. The manager added 1.8% above the risk-adjusted benchmark.
Frequently Asked Questions
Is generating alpha difficult?
Very. SPIVA reports consistently show 80–90% of active US large-cap funds underperform the S&P 500 over 10+ years, net of fees. Positive alpha is rare and often not persistent.
How is alpha different from raw return?
Raw return doesn't adjust for risk taken. A portfolio with 20% raw return but high beta may have LOWER alpha than a portfolio with 12% return and low beta. Alpha isolates skill from risk exposure.
Can alpha be negative?
Yes — very often. Negative alpha means the strategy performed WORSE than expected given its risk. High-fee active funds frequently exhibit chronic negative alpha.