Help with creating New Measure

[fbostan1]

I have a table I am working with to make Waterfall just like this Excel sheet 

I need to make few new measures before I can make it like look it excel sheet.

This is how my PowerBI looks like. 

The total numbers at the top matches to excel #issues numbers but the problem is when I choose each month, it gives me the count for that month. I want to subtrack the count of the month from the total and show the results.

For example, this is for month 0, I want to subtrack 564 from month Feb from total which is 21,163 to show in the next line.

[amitchandak]

@fbostan1 , refer my blog on the same

Cohort Analysis: https://community.powerbi.com/t5/Community-Blog/Customer-Retention-Part-3-Period-Of-Stay-Cohort-Anal...

or

https://youtu.be/Q1vPWmfI25o?t=749