Calculation gets bad performance when I add -1

Hi LotteLaugesen 

I'm assuming this is a measure.

You do have do watch out when adding a constant to a measure, as it means a value is returned for any combination of dimensions that might be included in a visual, potentially impacting performance.

Also, the outer CALCULATE is not needed if this is a measure.

I would try this:

VAR Ratio =
    DIVIDE (
        SUM ( FT_ManufacturingOrderHeader[Manufactured Quantity KG] ),
        SUM ( FT_ManufacturingOrderHeader[Kg Fillets] )
    )
RETURN
    IF ( NOT ISBLANK ( Ratio ), Ratio - 1 )

Alternatively, you could write this (should be equivalent):

VAR ManQtyKG =
    SUM ( FT_ManufacturingOrderHeader[Manufactured Quantity KG] )
VAR KGFillets =
    SUM ( FT_ManufacturingOrderHeader[Kg Fillets] )
RETURN
    DIVIDE ( ManQtyKG - KGFillets, KGFillets )

 Regards,

Owen