How Do You Make A Rolling Calendar Where The Hours Drop off After A Year

Hi,
I have been trying to create a Rolling Calendar spreadsheet and nothing I do seems to be working.

How Do You Make A Rolling Calendar Where The Hours Drop off after a year to the exact date?
Example hours were used on 4/13/12. How do you add those hours back to the Hours Remaining once it past 12 months (4/13/13)?

I really hope I am making since because I am really frazzled and confused right now. I attached a copy of the spreadsheet. If anyone could look at it and send me a formula or update my spreadsheet I would be extremely greatful.

Thanks,
Help - how to create a rolling calendar.xlsx

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