U.S. stocks are down only slightly for 2018, but that masks a volatile year for investors.

Trade-related tensions between the United States and China, weakness in the tech sector, concerns about slowing global growth and jitters about the Federal Reserve marching toward higher interest rates have kept investors on their toes.

Daily gyrations for the S&P 500 Index .SPX spiked sharply this year and remain near a one-year high.

One-month historical volatility - a measure of how much stocks have swung on a daily basis over the course of a month - has risen to 21 percent, up from about 7 percent a year ago.