A Function procedure returns a value. Call it from other code, or from a worksheet cell as a custom function when it lives in a standard module.

Code

Function Double(x As Double) As Double
  Double = x * 2
End Function

• Return a value

  Function Double(x As Double) As Double Double = x * 2 End Function → Assign to the function name to return

  =Double(A1) works in a cell.

• A Boolean helper

  Function IsWeekend(d As Date) As Boolean IsWeekend = Weekday(d, vbMonday) > 5 End Function → TRUE for Saturday and Sunday

  A tidy test reused everywhere.

• Wrap a pattern

  Function LastRow(ws As Worksheet) As Long LastRow = ws.Cells(ws.Rows.Count, 1).End(xlUp).Row End Function → The last used row of any sheet

  Wrap common patterns.

• Declare the return type after the closing parenthesis.
• Functions used in cells must not change other cells or formatting.
• Exit Function leaves early with the current return value.

• Forgetting to assign the function name returns 0 or an empty string.
• A cell calling a UDF shows #NAME? until macros are enabled.