How to count values at a certain date

Hello,

I am trying to create a dashboard for a service call system. In this system I have a Call date (open date) and a Close date. What i want to do is create a line graph which shows at what time how many calls were open.

I thought I could solve this by creating a Column which counts the rows where the Close date is smaller than the open date. This however doesn't work since it will just count all the rows since for one row the close date is never before the open date.

Is there a way to store the open date for one row and then count how many rows have a close date before said open date?

Thank you!