Calculated Columns using one year average and not calculating if prior year is missing

Hi janetcpa 

You're not dividing by 2 for the average equity in the sample data shown. Add the division by 2 if necessary here:

Avg Equity =
VAR previousYear_ =
    CALCULATE (
        MAX ( Table1[Fiscal Year] ),
        Table1[Fiscal Year] < EARLIER ( Table1[Fiscal Year] ),
        ALLEXCEPT ( Table1, Table1[Global Company Key] )
    )
RETURN
    IF (
        NOT ISBLANK ( previousYear_ ),
        Table1[Equity]
            + CALCULATE (
                SUM ( Table1[Equity] ),
                Table1[Fiscal Year] = previousYear_,
                ALLEXCEPT ( Table1, Table1[Global Company Key] )
            )
    )

ROE =
IF (
    Table1[Avg Equity] > 0,
    DIVIDE ( Table1[Net Income (Loss)], Table1[Avg Equity] )
)