Getting a undefined running total to a single cell

Hi...

I want to get the cumulative total of running values of several columns in to one cell in order the values are entered in the column cells. The issue here is I cannot define how many columns of values are to be predefined.

Please see the attached excel document. I need the values of L9,M9,N9,O9,P9,Q9,...........................N9.. to be added to H3...

I am guessing the # of columns the formula would reference would be dynamic, but what would that be based on? how would you determine how many columns to sum?

I am not sure I follow. I realize it may vary, but how it varies need to be decided by an input of some sort, whether it be a cell you input a number for the number of columns, or a row that indicates for each column whether you want it included, etc....
If you wanted to sum l9:q9 for example, it will obviously ignore blanks, so this only will matter if you have values in columns R-AP. If you have values in these columns, what will determine which column to stop at? Would the "input" row only have data in the columns you want summed?

Assuming cell I3 would define the # of columns to look at, this formula will work:

Formula:

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Try
=SUM($L$9: INDEX($L$9:$AP$9, MATCH(10^100, $L$9:$AP$9)))

The MATCH finds the last number in that row (9)
Is that what you are looking for?

I have NO idea why you wouldn't just use

Formula:

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(the blanks that follow the last column in row 9 will have no impact on the sum).
you have a formula that works, so... just go with it I guess. I am just curious what the difference is, that's all.

I was thinking the same thing, Melvin.

Thank goodness.
Worried I was missing something extremely obvious.
I suppose WE still could be. but... I'm not alone. Ha ha...