Vanguard offers data on the historical risk and return of various portfolio allocation models based on data from 1926 to 2018. For example, a portfolio consisting of 100% bonds has experienced an average annual return of 5.3%. Its best year, 1982, saw a return of 32.6%. It fell 8.1% in its worst year, 1969. Of the 93 years of historical data cited by Vanguard, a 100% bond portfolio lost value in 14 of those years.