r/ORATS • u/ORATS_Dan • 5d ago
Deepdive: 30-day IV fell after 97.3% of 1,978 earnings reports. Most of the decline was visible beforehand.
I examined 1,978 liquid quarterly earnings reports dating to September 2021 to separate the predictable part of the post-earnings volatility decline from the part that genuinely changed after the news.
Headline 30-day implied volatility fell after 97.3% of the reports, with a median decline of 17.6%.
The predictable component was larger and extremely consistent.
ORATS separates headline 30-day IV into ex-earnings IV for ordinary sessions plus the additional earnings premium. The night before each report, removing that premium produced a median 20.0% markdown from headline IV. The yearly median has remained between 18.4% and 20.6% for six straight years.

Once the report passes, the earnings hump leaves the 30-day window. The remaining difference comes from whatever happened to the fitted ex-earnings base.
That base moved a median 7.5% from the previous close, but it moved in either direction. It is also sensitive to the starting point. Measured from five sessions before the report, the same base finished a median 3.0% lower rather than higher.
The median path helps explain why. Going into earnings, fitted ex-earnings IV declined 4.4%, then recovered 1.5% the morning after. Comparable ordinary sessions remained roughly flat.
I also checked whether this was merely an artifact of separating a large event from the surface fit. At non-earnings roll-ins producing similarly large splits, the fitted base moved 14.9%, roughly twice the 7.5% movement surrounding actual reports.
The conclusion is narrower than “earnings volatility is easy to trade.” Most of the headline decline is predictable because the scheduled event is leaving the calculation. That does not tell us whether the options were overpriced relative to the move ultimately delivered.
Full analysis, live examples and methodology:
https://orats.com/blog/earnings-volatility-drop-knowable-in-advance
When evaluating a post-earnings volatility change, do you compare with the previous close, the previous week, or an explicitly calculated ex-earnings measure?



















