Convert UTC to local time and vice versa using VBScript

Today, I was stumbled upon UTC time conversions. I needed to convert UTC date/time to local date/time and vice versa. I was hunting this information everywhere with no luck.

I didn’t get the straight answer anywhere. So, I gathered all the info and created two VBScript based Functions. Hope it helps someone.

Here is the formula for converting time:

Local time to UTC: local time + (Bias / 1440 ) = UTC 
UTC to Local Time: UTC – (Bias/1440) = Local Time

Bias is available on the registry which tell what Time Zone is on the local computer. You can check the registry location at HKEY_LOCAL_MACHINESystemCurrentControlSetControlTimeZoneInformationActiveTimeBias

The ActiveTimeBias is the value of Bias/1400.

So, it came down to Adding the Bias to Local Time gives you the UTC time and Subtracting the Bias from UTC gives the local time.

Now the VBScript implementation of converting the times back and fourth.

‘*************************************************************************
‘ Name: ConvertToUTCTime ( sTime as Date )
‘ Parameters: Takes the Local Time. eg., 11/07/2006 10:00:00 AM
‘ Returns the converted UTC Time as 2006-11-07T18:00:000Z
‘
‘ Written by : Anand Venkatachalapathy
‘*************************************************************************
Function ConvertToUTCTime(sTime)

          Dim od, ad, oShell, atb, offsetMin
          Dim sHour, sMinute, sMonth, sDay

od = sTime
‘if you passed sTime as sting, comment the above line and
‘uncomment the below line.
‘od = CDate(sTime)

‘Create Shell object to read registry
Set oShell = CreateObject("WScript.Shell")

atb = "HKEY_LOCAL_MACHINESystemCurrentControlSet" & _
"ControlTimeZoneInformationActiveTimeBias"
offsetMin = oShell.RegRead(atb) ‘Reading the registry

‘Convert the local time to UTC time
ad = dateadd("n", offsetMin, od)

‘ If Month is single digit value, add zero
sMonth = Month(CDate(ad))
If Len(sMonth) = 1 Then
            sMonth = "0" & sMonth
End If

‘If Day is single digit, add zero
sDay = Day(CDate(ad))
If Len(sDay) = 1 Then
          sDay = "0" & sDay
End If

‘if Hour is single digit, add zero
sHour = Hour(CDate(ad))
If Len(sHour) = 1 Then
          sHour = "0" & sHour
End If

‘if Minute is single digit, add zero
sMinute = Minute(CDate(ad))
If Len(sMinute) = 1 Then
         sMinute = "0" & sMinute
End If

‘Assign the reutrn value in UTC format as 2006-11-07T18:00:000Z
ConvertToUTCTime = Year(CDate(ad)) & "-" & _
sMonth & "-" & _
sDay & "T" & _
sHour & ":" & _
sMinute & ":00Z"

End Function
‘ End of Function ConvertToUTCTime

‘*************************************************************************
‘ Name: ConvertToLocalTime ( sTime as Date )
‘ Parameters: Takes the UTC Time as 2006-11-07T18:00:000Z
‘ Returns the converted Local Time. eg., 11/07/2006 10:00:00 AM
‘
‘ Written by : Anand Venkatachalapathy
‘*************************************************************************
Function ConvertToLocalTime(sTime)

Dim od, ad, oShell, atb, offsetMin
Dim sHour, sMinute, sMonth, sDay
Dim ResultDate

‘Convert the UTC time 2006-11-07T18:00:000Z to
‘a normal date format 11/07/2006 10:00:00
‘Note the converted date would be 24 hr format
od = CDate( _
                     Mid(sTime,9,2) & "-" & _
                     Mid(STime,6,2) & "-" & _
                     Mid(STime,1,4) & " " & _
                     Mid(STime,12,8) _
                )

‘Create Shell object to read registry
Set oShell = CreateObject("WScript.Shell")

atb = "HKEY_LOCAL_MACHINESystemCurrentControlSet" & _
"ControlTimeZoneInformationActiveTimeBias"
offsetMin = oShell.RegRead(atb) ‘Reading the registry

‘Make the Bias as negative value. This step is required,
‘because VBScript offers only DateAdd function. I wish,
‘there is DateSubtract function in VBScript.
offsetMin = -(offsetMin)

‘Convert the UTC time to Local Time,
‘Note the OffsetMin is negative value
ad = dateadd("n", offsetMin, od)

‘ If Month is single digit value, add zero
sMonth = Month(CDate(ad))
If Len(sMonth) = 1 Then
                sMonth = "0" & sMonth
End If

‘ If Day is single digit value, add zero
sDay = Day(CDate(ad))
If Len(sDay) = 1 Then
              sDay = "0" & sDay
End If

‘ If Hour is single digit value, add zero
sHour = Hour(CDate(ad))
If Len(sHour) = 1 Then
              sHour = "0" & sHour
End If

‘ If Minute is single digit value, add zero
sMinute = Minute(CDate(ad))
If Len(sMinute) = 1 Then
            sMinute = "0" & sMinute
End If

‘ Gather up all fields and convert to a Date format
ResultDate = cDate(sDay & "-" & sMonth & "-" & Year(CDate(ad)) & " " & sHour & ":" & sMinute & ":00")

‘In the above step, ResultDate is in 24 hour format.
‘So convert into 12 hr format and assign the return value
ConvertToLocalTime = FormatDateTime(ResultDate,vbShortDate) & " " & FormatDateTime(ResultDate,vbLongTime)

End Function
‘End of ConvertToLocalTime Function