Calculate percentages for each month using multiple columns

Hi,

I'm wanting to create a column that calculates the percentage each month to a satisfaction survey with 5 possible responses.

Each row is currently time/date stamped and shows a singular response. 

There are 5 possible responses ranked 1-5 that make up the columns and each row also has a unique identifier.

When i create a chart (below) it groups the data by month and each bar in the chart shows one of the 5 responses; I want the format to be the same but for the chart to show percentage instead.  

How do I calculate the percentage (per month) in a calculated measure in Power BI? 

Thanks in advance :)