Create a forecast estimate updated with actuals weekly

Fri Apr 15 00:36:22 EDT 2016

Hi
Wondering if someone has this knowledge, and please forgive my maths expressions.
If I want to estimate need results to achieve a goal at the end of a term updated weekly with real results how would I structure this?
So as an example to illustrate my thought process(which could be wrong) These are Bills results for the first to weeks.
Bills Goal = 60% after 5 weeks.

	wk1	wk2	wk3	wk4	wk5
Bill	54.5%	57.1%			
So say these are the results that get it to current.
wk1		wk2	
get	opp	get	opp
6	11	4	7
So 6/11 etc
I am thinking to achieve this I then need to estimate an average opportunity rate rounded up. (11 + 7)/2 = 9 so if we had a 5 week term
wk3		wk4		wk5	
get	avgopp	get	avgopp	get	avgopp
X	9	X	9	X	9
So doing it manually I would discover Bill needs 6 out of 9 each week, which results in:
sumget	28	0.622222222	result
sumopp	45		
But how do I structure this so that the new results when known for week 3 update and adjust the following estimates?
Thanks
Sayth