KPI - Lead Conversion Rate

Hi, 

I've the folowing table with the name of all of our Customers and Potential Customers (Leads),     

In this table there is also the date the name was entered in our database as lead and the date this lead became an actual customer.

I want a measure that show for a specific date (used as filter in the report so it could be a specific month or a from ... to ... date)  the conversion rate (N. of inserted leads in this period / N. of converted leads, non necessarelly the same leads)

ES. in the first 10 month of 2020 4 leads were entered and 1 become a customer (25%). 

Thanks!