Need help CUMULATIVE active clients using start/end date

Hi all,

I have posted this question before but after some research and tips from the community I can explain the problem better.

I have a line chart that shows my active clients per year and month. The problem is that the chart only shows how many new clients I gained that year/month and not the new total.
So I need a formula that calculates when a client is active by looking at start agreement and end agreement. Now I depend on the agreement state column.
So the question is: Which Syntax(es) should I be looking at?

Because I know what needs to happen but I don't know how to do it.

This is the formula I have now:

Active clients =
CALCULATE(
    COUNT('Clients'[Client Code]),
    FILTER('Clients', 'Clients'[Price Agreement State] = "active"))

Sample data:

Thanks for the help in advance!