David Billigmeier wrote:
If your closing prices are in the range A1:A1023
put this formula in B2 and copy down: =A2-A1

You might note that that assumes that A1 is the
earlier closing price. If the OP downloaded Yahoo
historical quotes, for example, A1 would be the
later closing price. In that case, put =A1-A2
into B1:B1022.

Arguably, that should be "obvious'. But then
again, the same could be said for the OP's question.