Definition
Portfolio hedging is the practice of buying options on broad market instruments — index ETFs such as SPY, QQQ, DIA, IWM, or their respective futures-cleared cousins (SPX, NDX, RUT) — to protect a diversified equity portfolio against a systematic market decline. Rather than buying protective puts on each individual holding (which would be expensive, illiquid, and operationally complex), the investor hedges the aggregate market exposure with a single set of index contracts.
The size of the hedge is calibrated to the portfolio's market value. A $500,000 portfolio benchmarked to the S&P 500 might require roughly $500,000 of notional protection — which at an SPY price of $500 means ten contracts (each covering 100 shares × $500 = $50,000 notional). That sizing assumes a portfolio beta of ~1.0; higher-beta portfolios need more contracts, lower-beta need fewer.
The protection is imperfect by design. Index puts hedge only systematic risk — the part of returns that moves with the broad market. If the portfolio is heavily tilted toward small-caps, growth tech, or international stocks, the S&P 500 hedge will leave basis risk uncovered. The portfolio can lose money even when the index puts pay nothing, simply because the portfolio composition drifted from the hedge's reference index.
Why it matters
Tuning the protection level
Strike selection determines how deep a market move must go before the hedge pays off. An at-the-money put covers from current levels downward but is the most expensive. A 5%-OTM put functions like a 5% deductible — the portfolio absorbs the first 5% of loss, then the hedge engages. A 10%-OTM put is much cheaper but only activates after a meaningful drawdown. The right strike depends on risk tolerance, hedge budget, and the type of decline the investor is most concerned about. A retiree drawing income may prioritize floor protection (closer to ATM); a long-horizon accumulator may only want crash insurance (deep OTM).