Excel Cumulative Totals based on Dates

Hi

I am trying to create a cumulative total based on dates, but am having trouble doing so. I have tried a sumif formula, but it doesn't quiite work. Failing my suggestion below, perhaps its possible to have the cumulative total for such today, ie whats the cumulative total right now, rather than seeing the historic totals also

I have a start dates and end dates in format 23/09/2015 06:00:00. I have another column that has values next to it for each date range. I want a 4th column that tracks a running total of these values as dates come and drop off ie:

Start Date End Date Qty Cum Total
01/01/2015 01/03/2015 10 10
01/02/2015 02/02/2015 15 25
02/02/2015 06/02/2015 5 15
03/02/2015 05/02/2015 10 25
05/02/2015 06/02/2015 100 115
06/02/2015 07/02/2015 50 60

Your help would be much appreciated, many thanks

Adrian