Lookup and then sum a range

Im creating a spreadsheet that takes the year to date from the current year and compares it to the year to date from the same time last year (2013 v. 2012)

Am attaching the watered down spreadsheet for just one person (the final will have more than 50 listed).

I have been looking LOOKUP to find the current month stats but that year to date stat needw to be a sum of the range.

So in the example I changed the date so the month of May is the target (D1) >>=DATE(YEAR(TODAY())-1,MONTH(TODAY())*5,1)

I can get the value returned just for the month of May by using =LOOKUP, but what I need it to do is sum all totals from Jan through the month of May (B2:B6)
(I am setting this up so as the computer date changes (D1), the range will change to include all months from January through the current month.

Am somewhat a novice so stuck on which formula or how to write this, any help would be appreciated.

Mick