Index and Match or Vlookup with subtracting?

[worldCurrencies]

Hello, I have a spreadsheet that changes dynamically using the offset function. I want to be able to subtract in 1 column. I want to subtract the very last value in the last row by the first value.

For example:

In the image, please ignore column B. "Change in NFP", column C, is the column in which I'm trying to populate using index and match.
Right now, the formula for "Change in NFP" is = Ax - $A$18, where column A is "NFP Total". F18 is the last row, 144,431,000. However, when I change the time frame, F18 won't be the last row. How would I do this? I haven't done anything with index and match or vlookup, so if someone could provide the equation as well as explain it, I'd appreciate it. Thank you.

 

[Fluff]

Hi & welcome to MrExcel.
You can use this to get the last value in col A

=LOOKUP(2,1/($A$2:$A$10000<>""),$A$2:$A$10000)