Calculating Churn Rate on Cohort analysis show-case

DAX DAX Calculations
2

I think all the ingredients are there to achieve this.

For sales amount you likely just need to change the key calc in the below forumla - ‘Unique Customers’ to what sales amount you want.

Retention Period = 
VAR CustomerDimension = VALUES( Customers[Customer Names] )

RETURN
IF( SELECTEDVALUE( 'Cohort Periods'[Period] ) = 0, [Unique Customers],
CALCULATE(
  CALCULATE( [Unique Customers],
        FILTER( CustomerDimension,
            COUNTROWS(
                FILTER( 'Cohort Periods',
                    [Retention Days] > 'Cohort Periods'[Min Days] && [Retention Days] <= 'Cohort Periods'[Max Days] ) ) > 0 ) ),
                          TREATAS( VALUES( Dates[Month & Year] ), Customers[Join Month Cohort] ) ))

Then re-arrange the below formula with the updated formula above and then a ‘total sales’

Retention % = 
CALCULATE(
    DIVIDE( [Retention Period], [Unique Customers], 0 ),
        TREATAS( VALUES( Dates[Month & Year] ), Customers[Join Month Cohort] ) )

Everything is there in the example file from this session below.

I recommend going through this in detail and really understanding the concepts explained during this one.

Everything is there around the techniques required to get the answer you require for this. It just requires inputting what you require into the correct formula.