Sumif formula for a rolling 45 day period

[meilieng]

I am trying to sum a total number of sales in a given column for a rolling 45 day period. Column A = Dates , Column B = Sales, Column C= Total sales to date. However, the rolling 45 day period starts over every 45 days (i.e. Start date 09/26/2012 45 day rolling period ends 11/10/2012). Any help would be great on this. Thanks.