I'm not sure what the "rules" are for the date intervals you describe here:
So if I have a commitment due for $100 on Oct 1st, a commitment due on October 15th for $100 and a commitment due on Oct 30th for $100, it will show me in some kind of list view (or ideally some kind of Calendar view) that from October 1-14 I will have spent $100, by the 15th and until the 29th I will have spend $200 and by the 30th I will have spent $300.
You describe a 2 week interval (1-14) followed by a single day (the 15th) followed by another 2 week interval ( 15-29th) and then another single day (30th) and that opens up questions for February and months that are 31 days in length.
Can you provide just a bit more detail about exactly what you have in mind?
In my hypothetical scenario, if I only have 3 commitments in January for $100 each, by February my CommitmentsToDate should be a fixed $300. Should I have a commitment on any particular day in February, for say $100, on and after that day my CommitmentsToDate should be $400. The date intervals don't matter. So if I had more commitments spread out in October, each commitment would increase the CommitmentsToDate total from that day on.
This layout is part of a Film Production Management solution and the whole point of this Cash Flow chart is to assess how quickly I will deplete the funds in the bank. So for example, if I have $100,000 in the bank and next week I have many Commitments due that total $80,000 and the following week I have $20,000 due, I can deduce that I will need additional funding in two weeks, but I should be covered for next week.
Sounds like all you need is a summary field that totals your amount field with a running total.