Hi Silpa,
try this...it works!
You must create a properties in Time dimension containing the month number ( i used "BASE_PERIOD" )
Then, in dimension formula, use this one:
(([ACCOUNT].[ID],[MEASURES].[YTD])/([TIME].CURRENTMEMBER.PROPERTIES("BASE_PERIOD")))
the result will be your account value ytd / month number.
Hope this can help!
P.