Partial accumulation - need help

[#1]

I have a table as below:

Period                         Sales

Jan 2012	4,207.00
Feb 2012	4,247.00
Mar 2012	4,272.00
Apr 2012	4,272.00
May 2012	4,260.00
Jun 2012	4,132.00
Jul 2012	4,196.00
Aug 2012	4,189.00
Sep 2012	4,155.00
Oct 2012	4,159.00
Nov 2012	4,113.00
Dec 2012	4,053.00
Jan 2013	4,042.00
Feb 2013	4,001.00
Mar 2013	3,991.00
Apr 2013	4,030.00
May 2013	4,101.00
Jun 2013	4,062.00
Jul 2013	3,984.00
Aug 2013	4,019.00
Sep 2013	3,996.00
Oct 2013	4,086.00
Nov 2013	4,080.00
Dec 2013	4,081.00
Jan 2014	312.84
Feb 2014	312.84
Mar 2014	312.84
Apr 2014	161.81
May 2014	161.81
Jun 2014	161.81
Jul 2014	50.46
Aug 2014	50.46
Sep 2014	50.46
Oct 2014	-30.95
Nov 2014	-30.95
Dec 2014	-30.95

I need an expression that will use the numbers for 2012 and 2013 as is but will start adding 2014 numbers to its row above

so Jan 2014 (final value) = Dec 2013(table value) + Jan 2014 (table value)

  Feb 2014(final value) = Dec 2013(table value) + Jan 2014 (Table value) + Feb 2014(table value)

[jerem1234]

Hello, I used this formula:

if(Year(Period)=2014, rangesum(above(Sales,0,month(Period)+(Year(Period)-2014)*12+1)), Sales)

Let me know if this solves your issue. Please find attached qvw.

Hope this helps!