Hedges That Go Stale

A hedge is only as good as the relationship it relies on, and that relationship can drift after the hedge is put on. A classic example is a stock position hedged with an options position sized to a particular delta: as the underlying price moves and time passes, the option's actual delta changes (this is exactly what gamma measures), so a hedge that was neutral on day one can become badly under- or over-hedged weeks later if nobody rebalances it. The same problem shows up with pairs and index hedges, a stock hedged against a sector ETF because the two were historically 90% correlated can find that correlation quietly drop to 60% after a change in the company's business, leaving the position exposed to risk the hedge was supposed to remove, even though the trade blotter still shows a "hedged" position.

The practical fix is scheduled review rather than "hedge and forget": re-checking hedge ratios and the underlying correlation or delta assumption on a regular cadence, and treating any hedge older than that review window with suspicion until it's re-verified.

Staleness tends to creep in fastest around events that change the underlying relationship itself, an earnings surprise that shifts a stock's sensitivity to its sector, a merger announcement, or simply enough elapsed time for gamma to accumulate on an options hedge, so many desks also trigger an unscheduled hedge review whenever such an event occurs, rather than waiting for the next calendar checkpoint.