Average by Date and other criteria.

Hi Daniel and welcome to the forum

You could probably try using Averageifs() for this, but cannot say for sure without seeing some sample data and expected outcomes, to play with.
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How your expected result show as below

Date Cell EOE%
September 12 1 34%
September 12 2 18%

Can you please explain it ?

I am not entirely certain I understand what all you want in A3:C6. I shadowed those with these formulas in D3:F6.

Of note: those dates in column A of 'Calculates' are not dates. They are text that look like dates. If you are not aware of it dates are numbers starting with day 1= 1 - Jan - 1901. Today is 27 - Sept - 2018 or day 43370 from 1 - Jan - 1901. The formatting is cosmetic.

To coerce those text "dates" into their numeric values note the double unary "--" inside the MAX function. That is one method of coercion. Any math operator will have this effect.

	A	B	C	D	E	F	G	H	I
1	SHOW RESULTS
2	Date	No. Cell	EOE%	Date	No. Cell	EOE%
3	12-Sep	1	31%	12-Sep	1	31%	In D3: =MAX(--Calculates!$A$2:$A$11987)-COUNTIF($E$3:E3,E3)+1	In E3: =MOD(ROWS(E$3:E3)-1,2)+1	In F3: =AVERAGEIFS(Calculates!H:H,Calculates!A:A,D3,Calculates!D:D,E3)
4	12-Sep	2	47%	12-Sep	2	47%
5	11-Sep	1	34%	11-Sep	1	34%
6	11-Sep	2	45%	11-Sep	2	45%