Use DATEDIF formula in macros for unfixed cells (Eg, Cells (b, c))

[nicolenwn]

I need my macro to calculate the date difference between 2 ranges in 2 different sheets.

Ive got the codes below using record macro, however my range is not fixed as i'm using unfixed cells like (Cells (b, c)).

ActiveCell.FormulaR1C1 =
        "=DATEDIF(R[5]C,'production breakdown'!R[-5]C[1],""d"")"

I've tried

Cells(b, c) = DATEDIFF("d",(Cells(b,y)),'Production Breakdown'!B2)
&

Cells(b, c).FormulaR1C1 = "=DATEDIF(RC[-1],'Production Breakdown'!B2,""d"")"

But this doesn't work.