Expand range of offset/indirect formula to expand to entire range

Try this (simpler) array formula:

=OFFSET(INDEX($P$2:$OD$2,,MATCH(TRUE,P3:OD3<0,0)),,-1,1,1)

or a similar non-array version:

=OFFSET(INDEX($P$2:$OD$2,,MATCH(TRUE,INDEX((P3:OD3<0),0),0)),,-1,1,1)

Given your loaction, you may need ; as the spearator instead of ,

One of the main reasons that it did not work seems to be that you did not use EITHER of the solutions that I suggested...
This is the array formula that you used:

=OFFSET(INDIRECT(CELL("address",INDEX(P5:BE5,1,MATCH(TRUE,P5:OD5<0,0)))),ROWS($5:5)*-1,-1,1,1)

Apart from being totally different (!!) you did not $ the INDEX range.

Use this:

=OFFSET(INDEX($P$4:$OD$4,,MATCH(TRUE,INDEX((P5:OD5<0),0),0)),,-1,1,1)


If you want to get rid of the #N/A errors which appear when there are no negative values in the range, then use this:

=IFERROR(OFFSET(INDEX($P$4:$OD$4,,MATCH(TRUE,INDEX((P5:OD5<0),0),0)),,-1,1,1),"No Negatives")

Change the "No Negatives" to whatever error message you want to see, or use "" to return a blank.

You're welcome and thanks for the rep.