Turn monthly column data into Quarterly based on Date

[smartpat19]

Look up date and return the cell and the prior two columns (three columns total)

Data field:

[TABLE="width: 500"]
<tbody>[TR]
[TD]1/1/2019[/TD]
[TD]2/1/2019[/TD]
[TD]3/1/2019[/TD]
[/TR]
[TR]
[TD]10[/TD]
[TD]10[/TD]
[TD]10[/TD]
[/TR]
</tbody>[/TABLE]


Summary:

[TABLE="width: 500"]
<tbody>[TR]
[TD]3/1/2019[/TD]
[/TR]
[TR]
[TD]30 (formula)[/TD]
[/TR]
</tbody>[/TABLE]


Thank you

 

[Joe4]

I set up a simple example where the dates are in row 1, and the corresponding values are in row 2.
Then, if the value we want to look up is in cell F3, I put this formula in G3 to get my result:

=INDEX(2:2,0,MATCH(F3,1:1,0))+IFERROR(INDEX(2:2,0,MATCH(F3,1:1,0)-1),0)+IFERROR(INDEX(2:2,0,MATCH(F3,1:1,0)-2),0)