One way:

=IF(P10<0,SUM(M10:P10),"")

Given P10's formula, it could also be

=IF(P10<0, 2*P10+M10,"")

or, if you want to return 0 instead of a null string:

=(P10<0)*(2*P10+M10)


Note that the first "+" in your formula is superfluous.

In article ,
"Cheryl McHarg" <Cheryl wrote:

In my spreadsheet, I need cell L10 to sum cells ( M10-P10) if P10 does not
equal zero. P10 is a formula=+n10+O10.