Custom Fiscal Calendar

Thanks for sharing that eisbaer99 

Give this a go

UPDATE your table needed to be sorted first.

let
    TodaysRec = ExpandDate{ [Date = Date.From( DateTimeZone.FixedUtcNow()) ]}? ?? (error "Today's date is not included in the date table range"),
    Source = Table.FromRows(
        Json.Document(
            Binary.Decompress(
                Binary.FromText(
                    "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", 
                    BinaryEncoding.Base64
                ), 
                Compression.Deflate
            )
        ), 
        let
            _t = ((type nullable text) meta [Serialized.Text = true])
        in
            type table [#"Period Start Date End Date Weeks in Period Days in Period" = _t]
    ), 
    #"Removed blank rows" = Table.SelectRows(
        Source, 
        each ([Period Start Date End Date Weeks in Period Days in Period] <> "")
    ), 
    #"Changed Type to Text" = Table.TransformColumnTypes(
        #"Removed blank rows", 
        {{"Period Start Date End Date Weeks in Period Days in Period", type text}}
    ), 
    #"Split Column" = Table.SplitColumn(
        #"Changed Type to Text", 
        "Period Start Date End Date Weeks in Period Days in Period", 
        Splitter.SplitTextByDelimiter(" ", QuoteStyle.Csv), 
        {
            "Period Start Date End Date Weeks in Period Days in Period.1", 
            "Period Start Date End Date Weeks in Period Days in Period.2", 
            "Period Start Date End Date Weeks in Period Days in Period.3", 
            "Period Start Date End Date Weeks in Period Days in Period.4", 
            "Period Start Date End Date Weeks in Period Days in Period.5"
        }
    ), 
    #"Changed Field Type" = Table.TransformColumnTypes(
        #"Split Column", 
        {
            {"Period Start Date End Date Weeks in Period Days in Period.1", Int64.Type}, 
            {"Period Start Date End Date Weeks in Period Days in Period.2", type date}, 
            {"Period Start Date End Date Weeks in Period Days in Period.3", type date}, 
            {"Period Start Date End Date Weeks in Period Days in Period.4", Int64.Type}, 
            {"Period Start Date End Date Weeks in Period Days in Period.5", Int64.Type}
        }
    ),
    SortRows = Table.Buffer( Table.Sort(#"Changed Field Type",{{"Period Start Date End Date Weeks in Period Days in Period.2", Order.Ascending}})), 
    #"Renamed Headers" = Table.RenameColumns(
        SortRows, 
        {
            {"Period Start Date End Date Weeks in Period Days in Period.1", "Period"}, 
            {"Period Start Date End Date Weeks in Period Days in Period.2", "Start Date"}, 
            {"Period Start Date End Date Weeks in Period Days in Period.3", "End Date"}, 
            {"Period Start Date End Date Weeks in Period Days in Period.4", "Weeks in Period"}, 
            {"Period Start Date End Date Weeks in Period Days in Period.5", "Days in Period"}
        }
    ), 
    AddPeriodID = Table.AddIndexColumn(#"Renamed Headers", "Period ID", 1, 1, Int64.Type), 
    AddListDates = Table.AddColumn(
        AddPeriodID, 
        "Date", 
        each List.Dates([Start Date], [Days in Period], Duration.From(1)), 
        type {date}
    ), 
    ExpandDate = Table.ExpandListColumn(AddListDates, "Date"),
    AddPeriodOffset = Table.AddColumn(ExpandDate, "Period Offset", each [Period ID] - TodaysRec[Period ID], Int64.Type)
in
    AddPeriodOffset

I hope this is helpful