Divide 2 values filtered by date

Hello,

I tried searching around for similar solutions on this forum and other websites, but was unable to find a solution that works for my dashboard.

I am attempting to divide two filtered (by month and year) values from the same table. See display below.

As you can see, the values on the left are filtered by the chosen start date by the user while the values on the right are filtered by the chosen end date by the user. 

The date filter is located in a separate table from the data but linked to the original data table. The original data table is where the "Portfolio" and "Benchmark" values are stored. This is where I ran into trouble since these values are not measures, so I cannot simply create a third measure to divide one value by the other.

The arrows show which value I would like divided by the other. These would create a comparison between the rate of the Portfolio to the Benchmark.

Any tips you can recommend are appreciated!