The US stock market had its worst day since September 2022 this week, but for some investors, the move should not come as a surprise. That’s because the S&P 500 often experiences its most volatile days in August, a CNBC Pro study has revealed. Fears of a US recession were the main cause of this week’s global market meltdown. Investors are also worried that the Federal Reserve is backing away from cutting interest rates to ease the economic slowdown, with the central bank last week opting to keep rates at their highest level in two decades. Coincidentally, the summer month is second only to October as the most volatile day of the year since 1932, an analysis of FactSet data shows. One explanation for this is the low trading volume during the month, as many market participants enjoyed the sun on vacation rather than facing the trading terminal. On average, about 3 billion S&P 500 contracts traded daily in August, which was about 20% lower than in January, the month with the highest average trading volume, according to trading volume data dating back to 1999. While stock prices often swing dramatic. in August, the total return for the month – and the volatility they represent – is often in the middle of the pack. On average, stocks gained 0.5% in August, more than the average loss of 1.2% in December but lower than January’s big gain of 1.67%. August as a whole became the most volatile in just five years since 1928, compared to April, which spiked as the most volatile month in 15 different years. Methodology: The standard deviation of monthly price returns over a year is used to calculate monthly volatility.