Creating an Accurate Weekly Lead Report

Creating an Accurate Weekly Lead Report

Hi We have a workflow where we first create leads. Later once we establish communication we convert them into prospects.

Now when we have to generate a report on number of leads generated in  a particular week we are having a problem as leads once converted into prospects and no longer in leads. 

To get a report based on lead created date currently we first generate a report from leads then separate report from prospects and then coalated.

is there a better way to get this done?

thanks