The annualized rate is calculated by multiplying the change in rate of return in one month by 12 (or one quarter by four).
For example, if one month's rate of return is 0.25% and the next month's is 0.35%, the change in the rate of return from one month to the next is 0.10% (0.35-0.25). The annualized rate of return is equal to 0.10% x 12 = 1.2%.