Formula issue in spreadsheet every attempt causes wrong value

Hi Guys,

Wonder if any of you can help me out here.

Ive only ever built 1 excel file with formulas before and that wasnt as complex as this one im working on now.

Ive got to a point that i have tried and tried and tried to get the formula to work but i cant seem to get it right, ive attached the file in question but basically i cant figure what formula i need for this file.

Values inputted into column D should expire after 30 days so value in 1 should be removed at 30, value in 2 should be removed at 31 etc but also the value in column E should reflect that and also reflect the addition of any other value placed in column D all being under the same rule of expiring at 30 days.

Ive tried =E56-D1+D57 In the column and row where the value expires and ive tried dragging (by the lower right corner of the cell) but all that happens is the value "1" appears in ALL cells in that column.

Im stuck

Please help