@Nathaniel_C , I really appreciate your time and effort you put in. Please understand some of my previous calculations.
1 - I have a table name Active Users Data (Contain Invoice Date, Conversion Date, User ID's)
2 - I have calculated Measure total active users by using "Total Active Users = DISTINCTCOUNT('Active Users Data'[user_ids])"
3 - I have calculated Column Period by using "Period = DATEDIFF('Active Users Data'[User with Conversion Data.ConversionDate],'Active Users Data'[created_at],MONTH)".
4 - I have got this Table. Conversion Date / Active Users / Period, which tell me the customer retention.
5 - I have made the cohort Table the help of above table.
6 - For Calculating Churn in Need Period Month Users, that's what i looking for.
Please help you can. Hope I explained well this time