How do I use arrayformula on an IF formula?

Question

How do I use arrayformula on this formula?

=if(H3-H2=0,I2+B3,B3)

I would like to apply it to the whole I column...

Answer 1

I am not sure I understand exactly what you are after, but try this:

=arrayformula(if((H3:H15)-(H2:H14)=0,I2+B3,B3))

If you want the same result as dragging down your formula use:

=arrayformula(if((H3:H15)-(H2:H14)=0,(I2:I15)+(B3:B15),(B3:B15)))

Here is a link to my test spreadsheet. Your formula is in L2 and mine is in M2.