using a variable in a R1C1 formula

    ActiveCell.FormulaR1C1 = _
        "=(SUMPRODUCT(SUBTOTAL(3,OFFSET(RC[-7]:R[1000]C[-7],ROW(RC[-7]:R[1000]C[-7])-MIN(ROW(RC[-7]:R[1000]C[-7])),,1)),--(RC[-7]:R[1000]C[-7]>=0)))-1"

This formula works, but I’d like to change the R[1000] to R[iLastRow], but it doesn’t work.
Is there a way to include my iLastRow variable into the formula?

I’m counting the visible lines in a filtered list because I only want to print the listing if there is actual data.