Referencing a Cell Value That Changes with Filters

Hi everyone,

I have a data set that tracks expenditures by month and I wanted to create a new measure where I divide a calculated column by the sum of the expenditures in the twelve month. The sum of the expenditures in the twelve month would be the total expenditures for the year. I could just input that number manually, but I use a slicer where I filter by two departments, so the value is changing. I was wondering how I would reference a specific cell (sum of expenditures in the twelve month) in a DAX expression. 

I tried using FILTER but it only calculated it for the twelve row. I need it to calculate for every month using the sum of the expenditures in the twelve month as the denominator value.

Thanks