Excel 2007 : Summing Hours Within a Floating 90 Day Period

[Sumyunguy]

I work at a job requiring me to work 20 hours in a 90 day period. To track that, I am trying to create an excel spreadsheet that will tell me how many hours I have remaining in my requirement based on the previous 90 day period from a shift. I have columns for Shift Date, Hours Worked, and Hours Remaining.

I need help with a formula that will add up hours in the 90 days prior to the shift worked.

I have spent quite a bit of time scouring the internet and trying various sumifs and sumproduct formulas with no success. Any help is greatly appreciated!

Cheers

[dip11]

Can you upload a workbook with what you have currently?

Intuitively, I would say that since you are entering hours as you work into say column A you can have a cell in say C which is the 20 hours and a cell below that which has
=C-SUM(A:A)

When you add exact dates that gets a tiny bit more complicated where you need to check if the dates are within a certain range and subtract.

[Sumyunguy]

Sorry for the delay, here is the workbook, column B is for my reference as to when the hours worked "expire". I have been manually adding the hours remaining to meet the time requirements because I have not had a way to keep the total going with respect to the 90 day window.

Updated for correct file.