Cumulative Surplus/Deficit Monthly

BryanLy , You need to have date and then try

MTD Cumm= CALCULATE(SUM(Sales[Sales Amount]),DATESMTD('Date'[Date]))
last MTD Cumm= CALCULATE(SUM(Sales[Sales Amount]),DATESMTD(dateadd('Date'[Date],-1,MONTH)))

diff = [MTD Cumm]-[last MTD Cumm]

Date from month

date = "01-" & [Month] & "-" & [Year]

To get the best of the time intelligence function. Make sure you have a date calendar and it has been marked as the date in model view. Also, join it with the date column of your fact/s. Refer :
https://radacad.com/creating-calendar-table-in-power-bi-using-dax-functions
https://www.archerpoint.com/blog/Posts/creating-date-table-power-bi
https://www.sqlbi.com/articles/creating-a-simple-date-table-in-dax/

See if my webinar on Time Intelligence can help: https://community.powerbi.com/t5/Webinars-and-Video-Gallery/PowerBI-Time-Intelligence-Calendar-WTD-YTD-LYTD-Week-Over-Week/m-p/1051626#M184


Appreciate your Kudos.