The Post-Event Volatility Crush

Options on a stock reporting earnings, or on an asset ahead of a major scheduled event, trade with elevated implied volatility going into the event — the market is pricing in the uncertain, potentially large move that the event could cause. Once the event happens and the uncertainty resolves, that priced-in premium has no more reason to exist, and implied volatility drops sharply, often within minutes of the outcome being known. This is the "vol crush," and it happens whether or not the underlying moves much, which is exactly what catches unprepared options traders out.

Why the crush happens mechanically

Implied volatility reflects the market's expectation of how much the underlying will move, and ahead of a scheduled event that expectation has to account for a genuinely wide range of outcomes — the report could beat estimates, miss badly, or land in between, each with a real probability. Once the report is out, that entire distribution of possible outcomes collapses to a single realized fact, and there's no more event-specific uncertainty left to price into the option for that period. Implied volatility falls back toward whatever the "normal," non-event level is for that underlying — and because option prices depend directly on implied volatility, the option's value falls with it, independent of whatever the stock itself does.

A worked example

Suppose a stock trades at $100 the day before earnings, with 30-day implied volatility at 65% (elevated because of the event) versus a typical non-event level of 35%. A trader buys a straddle — a call and a put at the $100 strike — betting the stock will move enough to profit from the size of the move, not its direction. Say the stock actually moves only 2% after earnings, landing at $102, a modest, unremarkable move. But implied volatility crushes from 65% back to 35% within minutes of the report, and because both the call and put lose most of their volatility-driven value, the straddle can lose a large fraction of its cost even though the trader's basic view — "this stock will move" — was directionally correct. The move simply wasn't large enough to overcome the crush in the volatility that had been priced in.

What this means in practice

Traders who buy options specifically to bet on an event have to clear a higher bar than "the stock will move" — they need the realized move to exceed what was already priced into elevated implied volatility, because the vol crush works against them regardless. This is why some traders take the other side instead, selling options ahead of known events to collect the elevated premium, betting that the eventual move will be smaller than what's priced in — a trade with its own risk, since a genuinely large surprise move can overwhelm the premium collected many times over.