Formula to update Remaining values as actual values are entered

I am tracking plannning projects weekly (16 weeks), and from a total number of projects (195) i need to be able to see the decrease of projects over the period of weeks when the actuals are greater than the planned amount. i.e
( in week 1 my planned amount is 12.188)
My actual planned is 20.188 with a variance of -8
my week 2 is now 4.19 but how do i spread that -8 throughout my remaining weeks?
ultimately when my acutals are greater than my planned weekly i need it to decrease the number of remaining projects in the subsequent weeks.
that way i can see the actual week of completion.

thanks for your help in advance.