Rolling Targets Vs Actuals

Friends,
I wish to track my Weekly (Call & Meetings) Targets Vs Actuals over a period of one year (i.e. 52 weeks).
The difference between the two should be allocated over the remaining weeks thereby giving a clear and accurate picture of revised targets.
I have tried few formulas and tricks from the web but nothing has worked in favour.
Reqeuesting assistance in this regard.
Thanks in advance,
Anish