Two factors often determine stock prices in the long run: earnings and interest rates. Investors can't control the latter, but they can focus on a company's earnings results every quarter.Life and the stock market are both about expectations, and rising above what is expected is often rewarded, while falling short can come with negative consequences. Investors might want to try to capture stronger returns by finding positive earnings surprises.Now that we know how important earnings and earnings surprises are, it's time to show investors how to take advantage of these events to boost their returns by utilizing the Zacks Earnings ESP filter.The Zacks Earnings ESP, ExplainedThe Zacks Expected Surprise Prediction, or ESP, works by locking in on the most up-to-date analyst earnings revisions because they can be more accurate than estimates from weeks or even months before the actual release date. The thinking is pretty straightforward: analysts who provide earnings estimates closer to the report are likely to have more information.Now that we understand the basic idea, let's look at how the Expected Surprise Prediction works. The ESP is calculated by comparing the Most Accurate Estimate to the Zacks Consensus Estimate, with the percentage difference between the two giving us the Zacks ESP figure.In fact, when we combined a Zacks Rank #3 (Hold) or better and a positive Earnings ESP, stocks produced a positive surprise 70% of the time. Perhaps most importantly, using these parameters has helped produce 28.3% annual returns on average, according to our 10 year backtest.Most stocks, about 60%, fall into the #3 (Hold) category, and they are expected to perform in-line with the broader market. Stocks with a #2 (Buy) and #1 (Strong Buy) rating, or the top 15% and top 5% of stocks, respectively, should outperform the market, with Strong Buy stocks outperforming more than any other rank.Should You Consider Aflac?Now that we understand what the ESP is and how beneficial it can be, let's dive into a stock that currently fits the bill. Aflac (AFL) earns a #3 (Hold) right now and its Most Accurate Estimate sits at $1.31 a share, just 13 days from its upcoming earnings release on February 2, 2022.Aflac's Earnings ESP sits at 4.74%, which, as explained above, is calculated by taking the percentage difference between the $1.31 Most Accurate Estimate and the Zacks Consensus Estimate of $1.25. AFL is also part of a large group of stocks that boast a positive ESP. All of these qualifying stocks can be filtered by ESP, Zacks Rank, % Surprise (Last Qtr.), and Reporting date.Don't forget to head to the Earnings ESP Home Page. There, you'll find lots more earnings-related investing strategies to help build a winning portfolio.Find Stocks to Buy or Sell Before They're ReportedUse the Zacks Earnings ESP Filter to turn up stocks with the highest probability of positively, or negatively, surprising to buy or sell before they're reported for profitable earnings season trading. Check it out here >> Zacks Names "Single Best Pick to Double" From thousands of stocks, 5 Zacks experts each have chosen their favorite to skyrocket +100% or more in months to come. From those 5, Director of Research Sheraz Mian hand-picks one to have the most explosive upside of all. As one investor put it, “curing and preventing hundreds of diseases…what should that market be worth?” This company could rival or surpass other recent Zacks’ Stocks Set to Double like Boston Beer Company which shot up +143.0% in little more than 9 months and NVIDIA which boomed +175.9% in one year.Free: See Our Top Stock and 4 Runners Up >>Want the latest recommendations from Zacks Investment Research? Today, you can download 7 Best Stocks for the Next 30 Days. Click to get this free report Aflac Incorporated (AFL): Free Stock Analysis Report To read this article on Zacks.com click here.