dynamic sum function

[AliBb]

I have the following table I want the O/S column to calculate Total - sum(C4:?4)

? is determined based on the date in A2. In this example A4-sum(C4:C4) = 9000

If A2 = 31/8/18 then the formula would be A4-SUM(C4:D4).

How do I make this range dynamic?

	A	B	C	D	E
1
2	31/7/18
3	Total	O/S	Jul-18	Aug-18	Sept-18
4	10000	9000	1000	1000	1000

<tbody>
</tbody>

 

[Ron Coderre]

Using your posted example, try this regular formula:

B4: =A4-SUMIF($C$3:$N$3,"<="&$A$2,$C4:$N4)

Is that something you can work with?

 

[AliBb]

Thank you