Gamma Risk

A trader who is short an option benefits from gamma only as long as she rehedges perfectly. In reality, gamma risk is the cost of that imperfection—the losses that arise when the underlying moves faster than you can hedge, or when the true distribution of returns is fatter than your model assumes. For short volatility positions, gamma risk is the risk that gamma will eat you.

Why short gamma is a cost, not a benefit

A short option position has positive gamma—when the underlying moves, delta increases in your favour if you bought the option, or against you if you sold it. But that benefit is only theoretical if you can’t rehedge instantly. The moment you are short gamma, you are short the ability to buy low and sell high. Instead, you are forced to buy high and sell low: as the underlying rises, your short call becomes more in-the-money, so you must buy the underlying (at the higher price) to hedge; as it falls, you must sell (at the lower price). You realise losses on every rehedge.

The longer the moves and the wider the jumps, the worse this becomes. In volatility trading, gamma risk is the trader’s largest expense. An option desk that sells 100 vega of straddles is short 100 units of implied volatility but positive gamma. If realised volatility exceeds implied, the desk profits; but the path matters. Large, discontinuous moves force expensive, urgent hedges even if the total realised volatility ends up below the implied level.

Gamma accelerates around expiry

Gamma is highest when an option is at-the-money and close to expiration. This is the combination every short-gamma trader fears. A small price move changes delta by 50%, 75%, or even more on the final day. If you sold a call strike near the current price with one day left, you are sitting on a hair-trigger hedge. A 0.5% move in the underlying can require you to hedge a 30-contract swing. If the market is illiquid or you are large, that hedge costs real money—perhaps far more than the option is worth.

This is why options markets often spike in volatility the day or week before major corporate events (earnings, central bank decisions). Traders, conscious of ending gamma risk, demand higher option prices as insurance—they are paying for the privilege of avoiding the hedging costs they’d face if they sold.

Gamma and tail events

A second source of gamma risk is model risk. If you price an option assuming the underlying is normally distributed, you will underestimate the probability of large moves—the fat tails that reality produces. Real price returns are fat-tailed: 5% down days happen far more often than a bell curve predicts. When a 5% move happens, your gamma loss is far larger than your model thought it would be.

During the 2008 financial crisis and the 2020 COVID crash, traders who were short volatility were crushed. Models trained on 30 years of “normal” data failed to price the tail. Short-gamma hedges that seemed profitable on a 1% move were deadly on a 10% move. Volatility jumped so fast that dynamic hedges couldn’t execute; liquidity dried up; funding evaporated. The lesson: gamma risk includes the risk of model failure.

Gamma, leverage, and funding stress

A hedge fund or bank running a large short-volatility book will use leverage to maximise returns. But leverage amplifies gamma pain. If you are 10:1 leveraged on a volatility short and gamma eats $10 million in rehedging costs, you’ve wiped out 10% of your capital and face forced selling of hedges. Worse, if your funding is short-term or conditional on posted collateral, a realised gamma loss can trigger a funding squeeze—you can’t post collateral fast enough, your lender calls, and you are forced to exit at the worst moment.

This dynamic played a large role in the 2012 Knight Capital disaster, where a trading system left a short-volatility position unhedged overnight. A small market move turned into a $440 million loss within minutes because gamma accelerated losses faster than the system could hedge. Funding liquidity risk turned a recoverable trading loss into a death spiral.

Hedging gamma is expensive

The only way to avoid gamma risk is to buy gamma—in other words, to be long options. A portfolio manager worried about downside can buy puts, which are long gamma and will accelerate gains if the market crashes. A trader who wants to be long volatility can buy straddles or options outright. But long gamma is expensive: you pay the option premium, which includes a markup for the seller’s hedging cost plus their profit. The gap between what you pay and what the option eventually costs (via gamma losses) is the seller’s edge—it is profitable because gamma risk is real.

Monitoring gamma: the second derivative

Traders track gamma separately from delta for good reason. Delta tells you directional exposure; gamma tells you the cost of being wrong. A portfolio can be delta-neutral but hugely long gamma (bullish on volatility), or delta-neutral and short gamma (bearish on volatility). The Greeks let you separate these bets. If your risk model shows delta near zero but gamma large and negative, you are a volatility short—modest price moves won’t hurt you, but big moves will. This distinction is central to derivatives risk management.

See also