Retention cohorts are a marketeer's favourite tool. Here's a template for you to start measure it for your community.
Here's how you can use this template:
1) Click on the 'Framework Template'. It will take you to the Miro board.
2) Duplicate it to your workspace by clicking on the title of the board on top left corner. (you'll need to create an account on Miro if you don't have one - the free one should do)
3) Make the board your workbook to get this task done!