Excel - Applying formulae down a column and calculating a rolling sum

[ExGrunt]

@abcus1:

Cell a1.....=c38-d37
Cell a2.....=c39-d37
Cell a3.....=c40-d37

I now need to continue that sequence almost four hundred times for cell a4, a5, a6 etc., altering the formulae to c41-d37, c42-d37, c43-d37 etc

You need need to use an absolute reference to achieve this.

Normal excel references are 'relative' - ie:

If you have =A1+B1 in cell c1 and copy it down to c2 a relative reference will change relative to the copy eg =A2+B2.

Absolute references do not change at all. You tell excel to use absolute references by including a dollar sign $. You can 'fix' both the row and the column or just a row or a column. You can also have both absolute and relative references in a formula.

So using our example of a copy from c1 to c2:

= $A$1+$B$1 changes to = $A$1+$B$1
= A1+$B$1 changes to =A2+$B$1
= $A1+$B$1 changes to = $A2+$B$1

if you copied from c1 to d2 then:

= $A$1+$B$1 changes to = $A$1+$B$1
= A1+$B$1 changes to =B2+$B$1
= $A1+$B$1 changes to = $A2+$B$1

So in your example you need to enter in a1 : =c38-$d$37

Then copy it to the other cells.

EG