Macro to Identify Largest Value Across Columns, Then Subtract Value Held in Other Cell

give this a try

Sub Largest_Value_Highlight_Address()
'Determines largest values from the active worksheet

    Dim dataSet As String
    Dim rng As Range
    Dim sValue As Variant
    Dim Col As Range
    Dim iRow As Long
    Dim sAddress As Range
    Dim LastRow As Integer, x As Integer

    LastRow = Cells(999999, 1).End(xlUp).Row

    For x = 2 To LastRow
        dataSet = "I" & x & ":AS" & x
        Set rng = Range(dataSet)
        sValue = Application.WorksheetFunction.Max(rng)
        For Each Col In rng.Columns
            If Application.WorksheetFunction.CountIf(Col, sValue) > 0 Then
                iRow = Application.WorksheetFunction.Match(sValue, Col, 0)
                Set sAddress = Col.Cells(iRow, 1)
                sAddress.Select
                Cells(x, sAddress.Cells.Column).Value = Cells(x, sAddress.Cells.Column).Value - Cells(x, 69).Value
                With Selection
                    .Interior.Color = RGB(255, 255, 0)
                End With
            End If
        Next Col
    Next x

End Sub

Late entry ... ?

Option Explicit

Sub TMS()
Dim awf As WorksheetFunction: Set awf = WorksheetFunction
Dim rFound As Range
Dim i As Long

Dim lLR As Long
lLR = Range("A" & Rows.Count).End(xlUp).Row

For i = 2 To lLR
    On Error Resume Next
    Set rFound = Range("I" & i).Offset(0, awf.Match(awf.Max(Range("I" & i & ":AS" & i)), Range("I" & i & ":AS" & i), 0) - 1)
    With rFound
        ' prevent code running twice
        If .Interior.Color <> RGB(255, 255, 0) Then
            .Value = .Value - Range("BQ" & i).Value
            .Interior.Color = RGB(255, 255, 0)
        End If
    End With
    On Error GoTo 0
Next 'i

End Sub

Regards, TMS

Thanks for the rep