The answer by rix0rrr is great, but it does not support time zone offsets without colon or with only hours. I slightly enhanced the function to add support for these formats:

'--------------------------------------------------------------------- ' Declarations must be at the top -- see below '--------------------------------------------------------------------- Public Declare Function SystemTimeToFileTime Lib _ "kernel32" (lpSystemTime As SYSTEMTIME, _ lpFileTime As FILETIME) As Long Public Declare Function FileTimeToLocalFileTime Lib _ "kernel32" (lpLocalFileTime As FILETIME, _ lpFileTime As FILETIME) As Long Public Declare Function FileTimeToSystemTime Lib _ "kernel32" (lpFileTime As FILETIME, lpSystemTime _ As SYSTEMTIME) As Long Public Type FILETIME dwLowDateTime As Long dwHighDateTime As Long End Type Public Type SYSTEMTIME wYear As Integer wMonth As Integer wDayOfWeek As Integer wDay As Integer wHour As Integer wMinute As Integer wSecond As Integer wMilliseconds As Integer End Type '--------------------------------------------------------------------- ' Convert ISO8601 dateTimes to Excel Dates '--------------------------------------------------------------------- Public Function ISODATE(iso As String) ' Find location of delimiters in input string Dim tPos As Integer: tPos = InStr(iso, "T") If tPos = 0 Then tPos = Len(iso) + 1 Dim zPos As Integer: zPos = InStr(iso, "Z") If zPos = 0 Then zPos = InStr(iso, "+") If zPos = 0 Then zPos = InStr(tPos, iso, "-") If zPos = 0 Then zPos = Len(iso) + 1 If zPos = tPos Then zPos = tPos + 1 ' Get the relevant parts out Dim datePart As String: datePart = Mid(iso, 1, tPos - 1) Dim timePart As String: timePart = Mid(iso, tPos + 1, zPos - tPos - 1) Dim dotPos As Integer: dotPos = InStr(timePart, ".") If dotPos = 0 Then dotPos = Len(timePart) + 1 timePart = Left(timePart, dotPos - 1) ' Have them parsed separately by Excel Dim d As Date: d = DateValue(datePart) Dim t As Date: If timePart <> "" Then t = TimeValue(timePart) Dim dt As Date: dt = d + t ' Add the timezone Dim tz As String: tz = Mid(iso, zPos) If tz <> "" And Left(tz, 1) <> "Z" Then Dim colonPos As Integer: colonPos = InStr(tz, ":") Dim minutes As Integer If colonPos = 0 Then If (Len(tz) = 3) Then minutes = CInt(Mid(tz, 2)) * 60 Else minutes = CInt(Mid(tz, 2, 5)) * 60 + CInt(Mid(tz, 4)) End If Else minutes = CInt(Mid(tz, 2, colonPos - 2)) * 60 + CInt(Mid(tz, colonPos + 1)) End If If Left(tz, 1) = "+" Then minutes = -minutes dt = DateAdd("n", minutes, dt) End If ' Return value is the ISO8601 date in the local time zone dt = UTCToLocalTime(dt) ISODATE = dt End Function '--------------------------------------------------------------------- ' Got this function to convert local date to UTC date from ' http://excel.tips.net/Pages/T002185_Automatically_Converting_to_GMT.html '--------------------------------------------------------------------- Public Function UTCToLocalTime(dteTime As Date) As Date Dim infile As FILETIME Dim outfile As FILETIME Dim insys As SYSTEMTIME Dim outsys As SYSTEMTIME insys.wYear = CInt(Year(dteTime)) insys.wMonth = CInt(Month(dteTime)) insys.wDay = CInt(Day(dteTime)) insys.wHour = CInt(Hour(dteTime)) insys.wMinute = CInt(Minute(dteTime)) insys.wSecond = CInt(Second(dteTime)) Call SystemTimeToFileTime(insys, infile) Call FileTimeToLocalFileTime(infile, outfile) Call FileTimeToSystemTime(outfile, outsys) UTCToLocalTime = CDate(outsys.wMonth & "/" & _ outsys.wDay & "/" & _ outsys.wYear & " " & _ outsys.wHour & ":" & _ outsys.wMinute & ":" & _ outsys.wSecond) End Function '--------------------------------------------------------------------- ' Tests for the ISO Date functions '--------------------------------------------------------------------- Public Sub ISODateTest() ' [[ Verify that all dateTime formats parse sucesfully ]] Dim d1 As Date: d1 = ISODATE("2011-01-01") Dim d2 As Date: d2 = ISODATE("2011-01-01T00:00:00") Dim d3 As Date: d3 = ISODATE("2011-01-01T00:00:00Z") Dim d4 As Date: d4 = ISODATE("2011-01-01T12:00:00Z") Dim d5 As Date: d5 = ISODATE("2011-01-01T12:00:00+05:00") Dim d6 As Date: d6 = ISODATE("2011-01-01T12:00:00-05:00") Dim d7 As Date: d7 = ISODATE("2011-01-01T12:00:00.05381+05:00") Dim d8 As Date: d8 = ISODATE("2011-01-01T12:00:00-0500") Dim d9 As Date: d9 = ISODATE("2011-01-01T12:00:00-05") AssertEqual "Date and midnight", d1, d2 AssertEqual "With and without Z", d2, d3 AssertEqual "With timezone", -5, DateDiff("h", d4, d5) AssertEqual "Timezone Difference", 10, DateDiff("h", d5, d6) AssertEqual "Ignore subsecond", d5, d7 AssertEqual "No colon in timezone offset", d5, d8 AssertEqual "No minutes in timezone offset", d5, d9 ' [[ Independence of local DST ]] ' Verify that a date in winter and a date in summer parse to the same Hour value Dim w As Date: w = ISODATE("2010-02-23T21:04:48+01:00") Dim s As Date: s = ISODATE("2010-07-23T21:04:48+01:00") AssertEqual "Winter/Summer hours", Hour(w), Hour(s) MsgBox "All tests passed succesfully!" End Sub Sub AssertEqual(name, x, y) If x <> y Then Err.Raise 1234, Description:="Failed: " & name & ": '" & x & "' <> '" & y & "'" End Sub