IF statement calculated column

Hi Justas4478 ,

I recommend you to use SWITCH function instead of if statement.
Please try the bellow DAX code:

Order Day Adjustment = 
VAR Customer = 'Store Order data'[Customer]
VAR PGIDate = 'Store Order data'[PGI date]
VAR OrderDayDiff = 'Store Order data'[Order Day difference]
VAR BaseAdjustment = 
    SWITCH(
        TRUE(),
        Customer IN {"Stores UK", "Aldi", "Matalan", "Online", "Sandpiper", "TRS"}, -2,
        Customer = "Stores NI", -3,
        Customer = "Stores ROI", -5,
        0
    )
VAR AdditionalAdjustment = 
    SWITCH(
        TRUE(),
        WEEKDAY(PGIDate, 2) = 4, -3,  // Thursday
        WEEKDAY(PGIDate, 2) = 5, -2,  // Friday
        0
    )
RETURN
    OrderDayDiff + BaseAdjustment + AdditionalAdjustment