Why Does VBA Excel Keep Changing My Date Format to US Style?

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If you’ve ever tried to work with dates in Excel using VBA (Visual Basic for Applications), you may have run into a frustrating issue – your carefully formatted international dates keep getting changed to US date format (month first) when manipulated through VBA code. This can lead to incorrect dates, calculation errors, and general confusion. In this article, we’ll explain why this happens and provide several solutions to prevent Excel VBA from changing your date formats unexpectedly.

Understanding Excel’s Date System

To grasp why VBA causes dates to change format, it’s important to understand how Excel handles dates under the hood:

• Excel stores dates as sequential serial numbers so that they can be used in calculations.
• By default, January 1, 1900 is serial number 1, and January 1, 2008 is serial number 39448 because it is 39,448 days after January 1, 1900.
• Dates before 1900 are not supported.

This serial number system allows dates to be added, subtracted, and used in formulas just like regular numbers. For example, if you have a date in cell A1, you can add 7 to it to get the date a week later.

For display purposes, these serial numbers are then formatted as dates according to the cell formatting or system locale settings. This is why the same underlying serial number can display as “8/13/2023”, “13/08/2023”, “13-Aug-2023”, or other formats depending on your Excel settings.

Why VBA Changes Date Formats

The crux of the problem is that VBA uses the US date order (month-day-year) regardless of your Windows Regional Settings. So when you write VBA code to input a date, it will treat the date as being in month-first format.

For example, let’s say your computer is set to UK date format (day-month-year). In your worksheet, you enter the date 13/08/2023, which Excel interprets as August 13, 2023. But if you read that cell value into VBA using Range("A1").Value, VBA will interpret it as a US-style date and think you mean the 8th day of the 13th month. Since there is no 13th month, VBA throws a “Type mismatch” error.

The same issue occurs when writing dates from VBA to a worksheet. VBA will always use the US date order, so it ends up changing dates to the wrong value when it puts them in international date formatted cells.

This behavior can cause a lot of problems if your workbook uses non-US date formats. Imagine trying to calculate age from a birthdate or determine the number of days between two dates – if VBA is misinterpreting your date values, your formulas will return incorrect results.

Solutions to Prevent Date Formatting Issues

Thankfully, there are a few ways to get around this frustrating date conversion issue in VBA:

1. Use Unambiguous Date Formats

The simplest solution is to avoid ambiguity by always specifying dates in an unambiguous format, either with a 4-digit year or using named months:

• 4-digit years: Use formats like YYYY-MM-DD (2023-08-13) or DD-MMM-YYYY (13-Aug-2023). These cannot be misinterpreted regardless of locale settings.
• Named months: Use the Format() function to convert dates to a named month format that VBA will interpret correctly regardless of system settings:

  Format(myDate, "dd-mmm-yyyy") '13-Aug-2023
  Format(myDate, "dd/mmmm/yyyy") '13/August/2023

By using these unambiguous formats in your VBA code, you ensure that dates are always interpreted correctly.

2. Use DateSerial to Construct Dates

Instead of passing ambiguous date strings to VBA, use the DateSerial function to explicitly define the year, month and day parts:

DateSerial(2023, 8, 13) 'returns August 13, 2023

DateSerial takes three arguments – year, month, and day – and returns a valid Excel date serial number. This avoids any issues with string interpretation.

3. Convert String Dates Using DateValue

If you have a date in string format that you need to convert to a date value, use the DateValue function. This will convert the string to a date using the current system’s short date format.

DateValue("13/08/2023") 'returns August 13, 2023 on a UK system
DateValue("08/13/2023") 'returns August 13, 2023 on a US system

Be aware that DateValue will throw an error if the string is not in a format that matches the locale setting. To be safe, you can first convert strings to unambiguous formats:

DateValue(Format("13/08/2023", "yyyy-mm-dd"))

This ensures that DateValue will work correctly regardless of the system locale.

4. Write VBA to Detect System Date Order

For more complex international applications, you can make your VBA code more robust by detecting the current locale’s date order at runtime and adjusting your code accordingly.

Here’s a simple function to determine if the system is using month-first date format:

Function IsMonthFirstFormat() As Boolean
    Dim testDate As Date
    testDate = DateSerial(2000, 1, 2)

    If Format(testDate, "short date") Like "##/##/####" Then
        IsMonthFirstFormat = True
    Else
        IsMonthFirstFormat = False
    End If

End Function

This function creates a known date (January 2, 2000) and checks how it’s formatted in the system’s short date format. If the month comes first, it returns True, else it returns False.

You can then use this function to write conditional code that handles dates differently based on the system settings:

If IsMonthFirstFormat() Then
    'handle dates in US format
Else
    'handle dates in international format
End If

By incorporating this kind of locale awareness into your VBA code, you can create applications that work correctly with dates no matter where they’re run.

Final Thoughts

Excel’s US-centric VBA date handling is an unfortunate quirk that can throw a wrench in your international workflows. Misinterpreted dates can lead to calculation errors, data corruption, and hours of frustrating debugging.

However, by understanding how VBA treats dates, using unambiguous formats, and writing locale-aware code, you can avoid these date headaches. The key is to be explicit in your date handling, use the Format, DateSerial and DateValue functions strategically, and consider the current system settings when processing date values.

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Vaishvi Desai

Vaishvi Desai is the founder of Excelsamurai and a passionate Excel enthusiast with years of experience in data analysis and spreadsheet management. With a mission to help others harness the power of Excel, Vaishvi shares her expertise through concise, easy-to-follow tutorials on shortcuts, formulas, Pivot Tables, and VBA.