Option Explicit

' Вставьте весь код в обычный модуль VBA настольного Excel.
' Формула в ячейке: =RUBWORDS(A2)
' Сумма должна быть числом от 0 до 999999999999,99 и уже округлена до копеек.
Public Function RUBWORDS(ByVal amount As Variant) As Variant
    On Error GoTo BadValue

    If IsError(amount) Then GoTo BadValue
    If IsEmpty(amount) Then
        RUBWORDS = ""
        Exit Function
    End If
    If VarType(amount) = vbString Then
        If Len(Trim$(amount)) = 0 Then
            RUBWORDS = ""
            Exit Function
        End If
        GoTo BadValue
    End If
    If VarType(amount) = vbBoolean Or Not IsNumeric(amount) Then GoTo BadValue

    Dim value As Double
    value = CDbl(amount)
    If value < 0# Or value > 999999999999.99 Then GoTo BadValue

    Dim scaled As Double
    Dim totalKopecks As Double
    scaled = value * 100#
    totalKopecks = Fix(scaled + 0.5)
    If Abs(scaled - totalKopecks) > 0.000001 Then GoTo BadValue

    Dim rubles As Double
    Dim kopecks As Integer
    rubles = Fix(totalKopecks / 100#)
    kopecks = CInt(totalKopecks - rubles * 100#)

    Dim result As String
    Dim scaleIndex As Integer
    Dim group As Integer
    Dim groupWords As String
    For scaleIndex = 3 To 0 Step -1
        group = CInt(Fix(rubles / (1000# ^ scaleIndex)) - _
                     1000# * Fix(rubles / (1000# ^ (scaleIndex + 1))))
        If group > 0 Then
            groupWords = TriadWords(group, scaleIndex = 1)
            AppendWord result, groupWords
            Select Case scaleIndex
                Case 1
                    AppendWord result, FormOf(group, "тысяча", "тысячи", "тысяч")
                Case 2
                    AppendWord result, FormOf(group, "миллион", "миллиона", "миллионов")
                Case 3
                    AppendWord result, FormOf(group, "миллиард", "миллиарда", "миллиардов")
            End Select
        End If
    Next scaleIndex

    If rubles = 0# Then AppendWord result, "ноль"
    AppendWord result, FormOf(rubles, "рубль", "рубля", "рублей")
    AppendWord result, Format$(kopecks, "00")
    AppendWord result, FormOf(kopecks, "копейка", "копейки", "копеек")

    RUBWORDS = UCase$(Left$(result, 1)) & Mid$(result, 2)
    Exit Function

BadValue:
    RUBWORDS = CVErr(xlErrValue)
End Function

Private Function TriadWords(ByVal number As Integer, ByVal female As Boolean) As String
    Dim unitsMale As Variant
    Dim unitsFemale As Variant
    Dim teens As Variant
    Dim tens As Variant
    Dim hundreds As Variant
    unitsMale = Array("", "один", "два", "три", "четыре", "пять", "шесть", "семь", "восемь", "девять")
    unitsFemale = Array("", "одна", "две", "три", "четыре", "пять", "шесть", "семь", "восемь", "девять")
    teens = Array("десять", "одиннадцать", "двенадцать", "тринадцать", "четырнадцать", _
                  "пятнадцать", "шестнадцать", "семнадцать", "восемнадцать", "девятнадцать")
    tens = Array("", "", "двадцать", "тридцать", "сорок", "пятьдесят", _
                 "шестьдесят", "семьдесят", "восемьдесят", "девяносто")
    hundreds = Array("", "сто", "двести", "триста", "четыреста", "пятьсот", _
                     "шестьсот", "семьсот", "восемьсот", "девятьсот")

    Dim remainder As Integer
    Dim digit As Integer
    Dim result As String
    digit = number \ 100
    If digit > 0 Then AppendWord result, CStr(hundreds(digit))
    remainder = number Mod 100
    If remainder >= 10 And remainder <= 19 Then
        AppendWord result, CStr(teens(remainder - 10))
    Else
        digit = remainder \ 10
        If digit > 0 Then AppendWord result, CStr(tens(digit))
        digit = remainder Mod 10
        If digit > 0 Then
            If female Then
                AppendWord result, CStr(unitsFemale(digit))
            Else
                AppendWord result, CStr(unitsMale(digit))
            End If
        End If
    End If
    TriadWords = result
End Function

Private Function FormOf(ByVal number As Double, ByVal one As String, _
                        ByVal twoToFour As String, ByVal many As String) As String
    Dim lastTwo As Integer
    Dim lastDigit As Integer
    lastTwo = CInt(number - 100# * Fix(number / 100#))
    lastDigit = CInt(number - 10# * Fix(number / 10#))
    If lastTwo >= 11 And lastTwo <= 14 Then
        FormOf = many
    ElseIf lastDigit = 1 Then
        FormOf = one
    ElseIf lastDigit >= 2 And lastDigit <= 4 Then
        FormOf = twoToFour
    Else
        FormOf = many
    End If
End Function

Private Sub AppendWord(ByRef result As String, ByVal word As String)
    If Len(word) = 0 Then Exit Sub
    If Len(result) > 0 Then result = result & " "
    result = result & word
End Sub