Formula to grab item count from the last recorded date to find the difference

I have a simple Excel sheet with a Formatted Table where I am tracking the count of a variable in an experiment. I record this count at the beginning of every day when I have the opportunity to do so. There are some days where I do not have the opportunity to record count.

Date	Count
7/5/2018	45
7/6/2018	41
7/9/2018	40
7/10/2018	42
7/11/2018	49
7/12/2018	55
7/13/2018	53
7/16/2018	54
7/17/2018	58

I want to add a third column to this formatted table where it finds the net growth between [@Count] and the Count of the previously recorded date. I am familiar with the usage of INDEX(MATCH()), it's just that I don't know how to write into a formula to look for "the previous date" (rather than statically look for [@Date]-1), I do not know what formulas could help me do this.

Can you add a few lines when you can't make records and the expected result in third column?

Since the previously recorded date is directly above the most recent one, why not keep it simple and have something like this:

C2 =IFERROR(B2-B1,"")

This assumes that "Count" is in column B and that your data starts in row 2 (headers in row 1).

In that case, consider creating a small representative sample where the suggestion above wouldn't work along with the desired results (which can be entered manually).

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