Report Builder - Running total

Hi,

I have scheduled report builder report which periodically (weekly) sends me data on selected activity. Alongside this, my client has now asked for a running total, so alongside the periodic (weekly) reporting they can also see the total performance since activity started.

 I'm wondering how best to do this in report builder. I basically want to anchor my start date, but have a rolling end date.

So, assuming the activity started on 01/01/2016 I want to set up a report which will show data from 01/01/2016 to date, without having to manually update the dates each week.

I've had a play with the customise date expression, but I can't seem to get it to work. In my head it would look something like this;

Start Date: 01/01/2016

End Date: cd-1

Has anyone come across this before?

Thanks

Toby