Entering values based on start date

BGamble 

It's not altogether clear what you're asking, and how the sample spreadsheet represents it. Among other things that are ambiguous, your labels in the spreadsheet are "Need" and "Want" with the former sounding more urgent (higher priority) than the latter, but I don't really think that's what you mean.

Anyway, it might be that your solution is to be found in the use of the MIN function, coupled with a separate or added line of figures above the calendar quarters, the added line showing the percent to be added as part of that ramping up. Here's an example

=MIN($E16,G16+($E16*H11))

Take a look at the attached, play around with the ramping up percentages (by the way, I added ones beyond the point of 100%, just to make sure the numbers stopped growing.