You also need to account for reinvested distributions, return of capital, and other factors. (moneysense.ca)
(For an excellent explanation of reinvested distributions in mutual funds, see page 10 of this guide from RBC.) (moneysense.ca)
Year - to - date figures are not annualized and represent total return, which includes reinvested distributions (income and capital gains) and any change in unit price for the given period. (maryland529.com)