Count uniqe values existing in two variable tables

Hi, I have two connected tables.

The first one (Table1) cointains sales data with unique client ID and date among other things. The second one (Table2) is a simple table with dates.

I'm trying add a new column to the second table, where for each date there is a percentage of returning clients from the previous month. Here is the code:

ReturningCustomers=

Var startDate = /// (logic counting beginning of the last month)

Var endDate = ///  (logic counting end of the last month)

Var lastMonth = CALCULATE( DISTINCTCOUNT(Table1[ClinetID]); FILTER( Table1; [Date]>=startD && [Date]<=endD ) )

Var lastMonthColumn = CALCULATE( DISTINCT(Table1[ClinetID]); FILTER( Table1; [Date]>=startD && [Date]<=endD ) )

Var currMonthColumn = CALCULATE( DISTINCT(Table1[ClinetID]); FILTER( Table1; [Date]=Table2[Date] ) )

Var X = ??? (number of unique values existing in both lastMonthColumn and currMonthColumn)

Return

X/lastMonth

The problem is I don't know how to find number of unique values existing in both tables - variable X?

Sample data

Table1:

Table2:

The expected result is:

So 2/3 clients returned