One of the foundational assumptions in investing is that share prices adjust quickly when important information becomes public. A company reports earnings ahead of expectations, the shares rise and the good news appears to be fully reflected immediately.
Yet, decades of research suggest the process is not always so neat. Companies that deliver unexpectedly strong earnings have historically tended to outperform for a period after the announcement, while those reporting negative surprises have often continued to underperform. Researchers call this phenomenon post-earnings-announcement drift (PEAD).
For investors, the opportunity may arise when a strong result signals that the market has not yet fully adjusted its expectations for a company's future earnings. The information is not secret. Everyone can read the result. The interesting part is that investors may take time to work out what the result means for the years ahead.
The first move is not always the last
Suppose analysts expect a company to earn $1.00 per share and it reports $1.15. Its share price might rise 8% on the day. The market has clearly responded, but investors still have to decide whether the extra 15 cents was simply temporary, or evidence of a more durable change.
Perhaps margins are improving faster than expected, a new product is gaining traction, or pricing is holding up better than analysts assumed. If the improvement is sustainable, the result does more than lift the current year's earnings. Forecasts for next year, and possibly the year after that, may also need to rise.
The market therefore faces two questions: react to the reported surprise, then reassess the company's longer-term earnings power. The first is answered almost instantly. The second can take weeks, months or even multiple reporting periods.
The surprise is measured against expectations
A company's results matter relative to what investors already expected. A business can report 30% earnings growth and see its shares fall because the market expected 40%. Another can report declining earnings and rally because the decline was much smaller than feared.
This is why earnings growth, considered on its own, can be misleading. Investors also need to ask what level of growth is embedded in the valuation and whether the latest evidence supports that assumption.
Results season provides a regular scorecard. When reality is materially better than expected, the useful question is not simply whether the company beat the number. It is whether the market has fully adjusted its view of what comes next.
Why forecasts adjust slowly
Academic studies have documented PEAD for decades. The central finding was simple: share prices did not always fully reflect what current earnings implied about future earnings. The finding has since been examined across different markets, periods and methods.
Behavioural anchoring is one possible explanation. Analysts and investors spend months developing forecasts. When fresh evidence arrives, they may revise those estimates in stages rather than discard the old framework at once. A forecast of $2.00 may move first to $2.20, then to $2.35 as further evidence confirms the change, even if the underlying business is already heading towards $2.50.
There is also a practical institutional dimension. Large investors rarely rebuild a position immediately. A portfolio manager may need to review the result, test the assumptions, speak with analysts and assess valuation before committing more capital. Information can become public instantly while portfolios respond more gradually.
Separate a beat from an inflection
None of this means investors should buy every company that beats consensus estimates. The quality and source of the surprise matter. A result supported by stronger revenue, improving margins and upgraded guidance usually carries more information than one produced by a tax benefit, delayed expenditure or a short-term cost reduction.
Research by Narasimhan Jegadeesh and Joshua Livnat found that the post-announcement effect was stronger when revenue and earnings surprises pointed in the same direction. That is intuitive: sustained revenue strength is generally harder to manufacture than a one-quarter earnings beat.
Cash flow should confirm the reported earnings. Investors should also examine orders, customer numbers, pricing, volumes and management's guidance. The aim is to decide whether the result changed the likely earnings path over several years, rather than merely shifted profit between quarters.
This is the difference between an earnings surprise and an earnings inflection. A surprise may disappear at the next result. An inflection can change the value of the business.
The second surprise can be more revealing
The most compelling bases involve companies whose earnings are repeatedly underestimated. It reports ahead of forecasts, analysts raise their estimates and, three months later, it beats the higher hurdle again.
This pattern can occur when a company enters a period of rising margins, gains market share, launches a successful product or benefits from a structural change that investors initially underestimate. By the third or fourth result, the market may accept that the old assumptions no longer fit.
In these situations, the real significance of the first beat is not the additional profit delivered in that quarter. It is the possibility that the market's assumptions about the business have been fundamentally wrong.
Valuation still sets the terms
There is an obvious risk in following earnings momentum. A good result can attract an expensive price. Once expectations move from too pessimistic to excessively optimistic, the process can reverse. A company priced for perfection has little room for an ordinary result, let alone a disappointment.
Earnings surprises should therefore complement fundamental analysis, not replace it. Competitive position, balance-sheet strength, cash generation, management quality and valuation still determine whether the shares offer an acceptable risk-reward trade-off.
The historical PEAD effect also varies across periods and markets. Trading costs, liquidity and the precise timing of information can reduce returns, particularly in smaller companies. Treating the research as a mechanical trading rule misses the point. Its better use is as an analytical clue: a strong result may contain more information than the first day's price move suggests.
Follow the direction of expectations
Investors devote enormous effort to forecasting the future. An equally important question is which companies are demonstrating, through their reported results, that today's forecasts are wrong.
When a business repeatedly exceeds expectations, improves its outlook and forces analysts to lift forecasts, investors should pay close attention. The market is forward-looking, but expectations can be sticky. Sometimes the most valuable information in a result is not what the company earned last quarter. It is what the result tells us about earnings still to come.
Selected research
1. Bernard, V. and Thomas, J. (1989), 'Post-Earnings-Announcement Drift: Delayed Price Response or Risk Premium?', Journal of Accounting Research. View source
2. Bernard, V. and Thomas, J. (1990), 'Evidence that Stock Prices Do Not Fully Reflect the Implications of Current Earnings for Future Earnings', Journal of Accounting and Economics. View source
3. Jegadeesh, N. and Livnat, J. (2006), 'Revenue Surprises and Stock Returns', Journal of Accounting and Economics. View source
Jarrad Stuart is Portfolio Manager at Sharpbridge Funds Management (ABN 14 676 769 538, AFSL 561296), a Brisbane-based global equities boutique. This article contains general information only and does not take into account any person's objectives, financial situation or needs. It is not personal financial advice. Readers should consider obtaining professional advice before acting on the information.