In the US, the biggest one-year drop in the Global Financial Data extension of Moody's monthly total return index for 30-year corporate bonds (going back to 1857) was 12.5% in the 12 months ending in February 1980. Compare that to the stock market: According to the GFD monthly S&P 500 total return index, an annual loss of 67.8% occurred in the year ending in May 1932, during the Great Depression, and one-year losses have exceeded 12.5% in 23 separate episodes since 1900.