Daily cumulative average inventory value

Hi,

I'm trying to figure out a way to re-write the following formula. The end result should be an average of the closing balance for the past 365 days.

Here is the closing balance forumla

Closing Balance:=

VAR MaxDate = MAX('Date Dimension'[Date]) RETURN

CALCULATE(
    IF(ROUND(SUM([Extended Cost - Modified]);2)=0;BLANK();ROUND(SUM([Extended Cost - Modified]);2));
    'Item Ledger'[Date - For G/L (and Voucher)]<= MaxDate
)

Here is a an example of what I would like to achieve, but I cant figure out the dax syntax

Average Daily Balance:=

VAR MaxDate = MAX('Date Dimension'[Date]) RETURN

VAR i = 0;
VAR total = 0;

DIVIDE(
    do {
        total = total + CALCULATE(
        IF(
            ROUND(SUM([Extended Cost - Modified]);2)=0;
            BLANK();
            ROUND(SUM([Extended Cost - Modified]);2));
            'Item Ledger'[Date - For G/L (and Voucher)]<= MaxDate - i
        )
        i++
    } while ( i < 365 );
    365
)

How would I go about writing this?