Rolling Balance after 30 days

[excelrookie05]

Hello all,

I have a project that requires a rolling balance after a 30 day period.

Ex: On 7/1/05 the starting balance is 50,000.
7/4/05, 10,000 is removed
7/18/05, 10,000 is removed
7/29/05, 10,000 is removed.

Now I need the amount subtracted on these days to be added back to the balance after 30 days, so ...

8/4/05, 10,000 gets addded back to the balance,
8/18/05, 10,000 gets addded back to the balance,
8/29/05, 10,000 gets addded back to the balance,

Is there a way to formulate this?