You can create this by putting one of your date fields into columns, then right click and select month. I would recommend the month in the green highlighted area below:
Having it as green means it's continuous and I think it's better for time lines.
Next bring ID into the rows shelf and right click and change it to a measure - use count or count distinct:
Ultimately you'll get this view:
I've attached the workbook with the example.
Members_v10.2.twbx 587.8 KB
thanks for replying，but this is just how many "new" member join in each month，i want how many current members in every month，is it possible to do?
I have the same question, if anyone finds an answer.
Please find my solution attached.
Below is the steps
1st, inner join your data with a calendar table by using the key 1=1
2nd, create 3 calculation fields as below
3rd, build the view
Hope this helps
Book1_v10.2.twbx 628.3 KB
Brilliant, thank you! I had to adapt the filter as I had some Null leaving dates, but otherwise perfect.