Formula to calculate value of column at End of Month

Hi there,

I was hoping for some help to calculate the value of a column without going in and manually subtracting values!

Please see attached for example.

In the attached on sheet 1, I have the value of the whole of column A from sheet 2 under Apr 18

For May 18, you will see I have the same, but went into sheet 2 and deducted the values where the exit month is May 18.

Is there a way of doing this to automatically value the totals with deducting the value as each month occurs?

Any questions, please do not hesitate to ask.

Your help would be much appreciated.

Regards

N