Adding flexibility to a forecast

[MontanaAggie]

I am trying to create a calculation that if I change a date, it'll update the forecast. It's hard for me to describe so I have attached an example.

Basically I have 12 months that need to be populated with budget amounts. Depending on the month the spud date occurs, is when I want the calculation in the forecast (shaded light blue) to begin. The only input I want to change is the spud date (shaded in yellow). Currenlty I have forced the months to match on Wells 1 & 2, but I want to have the flexibility to change the spud date and subsequent equations would be updated.

[shg]

      ---A--- ----B----- --C--- D ----E----- ----F----- ----G----- ----H----- ----I----- ----J----- ----K----- ----L----- ----M----- ----N----- ----O----- ----P-----
  1                               Month 1    Month 2    Month 3    Month 4                                                                                           
  2                                      50%        30%        20%        10%                                                                                        
  3                                                                                                                                                                  
  4           Spud Date  Budget   01/31/2012 02/29/2012 03/31/2012 04/30/2012 05/31/2012 06/30/2012 07/31/2012 08/31/2012 09/30/2012 10/31/2012 11/30/2012 12/31/2012
  5   Wells 1 02/15/2012   5000                    2500       1500       1000        500                                                                             
  6   Wells 2 03/20/2012   7500                               3750       2250       1500        750                                                                  
  7   Wells 3 04/30/2012   6000                                          3000       1800       1200        600                                                       
  8   Wells 4 05/15/2012   2500                                                     1250        750        500        250                                            
  9   Wells 5 07/09/2012   4000                                                                           2000       1200        800        400

Note the blank column D.

The formula in E5 and copied down and across in

=IF(OR(EOMONTH($B5, 0) > E$4, COUNT($D5:D5) > 3), "", $C5 * INDEX($E$2:$H$2, COUNT($D5:D5) + 1))

Note also that the numbers in row 2 don't add to 100%.