Earnings Season and Index Volatility

Index traders do not need to follow every company, but they cannot ignore earnings season. For several weeks each quarter, the largest companies in an index report results, and the pattern of surprises shapes the index as much as any macro release.

Why it moves the index

A size-weighted index is dominated by its largest members. When a handful of them report, the reaction in their shares moves the index directly. Beyond that, results from one company change expectations for its peers, so a strong report in one sector lifts the whole sector before the others have reported. The season therefore produces both single-day jumps and multi-week drifts.

Reading the season

Three questions matter for the index:

• Are most companies beating or missing expectations? The share of beats is reported through the season and sets the tone.
• How are shares reacting to beats? When good results produce falls, expectations were too high and the index is vulnerable.
• What are companies saying about the coming quarter? Guidance moves expectations for the next season more than the results move the current one.

The second question is the most useful. A season in which beats are sold is a late-cycle sign; a season in which misses are bought suggests the bad news was already priced.

The calendar

The largest companies tend to report in a cluster, and the days around those reports are where the index risk sits. Mark them. A report after the close produces a gap at the next open; a report before the open feeds straight into the first hour. Index contracts react during the extended hours when the cash market is closed, so holding a position through a major report is holding through a gap.

Volatility pattern

Implied volatility usually rises into the season and falls once the largest companies have reported, because uncertainty is resolved. Trend strategies on indices tend to do better in the second half of the season, once the direction set by the leaders is established. Range strategies suffer in the first half, when gaps are frequent.

A strategist who trades indices should say how they handle the reporting calendar. Holding full size through the largest reports is a choice that produces larger drawdowns; standing aside is a choice that misses some moves. Neither is wrong, but the disclosure should say which.

What to watch

Watch the share of companies beating expectations, the reaction of shares to beats and misses, the guidance tone, and the calendar of the largest reports. The index direction for the following month is often visible by the midpoint of the season.