VBA & Macro Problems

How to Access and Use a VBA Module Function in Microsoft Access

Kushani Nimanthika Sep 30, 2026 868 views

Question details

The user needs to correctly call and use a user-defined VBA module function without triggering availability or undefined errors.

How to Access and Use a VBA Module Function in Microsoft Access

Product: Microsoft Access
Device & OS: not provided
Scenario: Attempting to execute or call a custom VBA function from an Access macro, query, or form.
Observed behavior: The user-defined function is not available, cannot be found, or throws an error due to spelling mistakes, incorrect scope declarations, or missing VBA library references.

Before you start

Before modifying your database code, carefully check your macro or query for any simple typing errors in the function name, as overlooked typos are the most common cause for this issue.

Solution 1Recommended

Declare the VBA Function as Public

To make a custom function accessible throughout your entire Access database, it must be explicitly declared with the Public scope inside a standard module.

By default, functions may be restricted to the module they are created in. Declaring a function as Public ensures that queries, forms, and macros across the database can interact with it.

Open the VBA Editor

Press Alt + F11 on your keyboard while inside Microsoft Access to open the Visual Basic for Applications (VBA) editor.

Locate the Standard Module

In the Project Explorer pane on the left, find the module containing your function under the 'Modules' folder.

Update the Function Declaration

Ensure your function definition starts with the word Public. For example, change 'Function MyFunction()' to 'Public Function MyFunction() As Variant'.

Compile the Database Project

Click on 'Debug' in the top menu bar, then select 'Compile [Your Database Name]'. This verifies the code and saves the changes.

Naming Tip: Ensure that the name of your standard VBA module is not exactly the same as your function name, as this conflict can also make the function unavailable.

Solution 2

Check and Add Missing VBA References

If your function relies on external libraries or is stored in a separate database file, you must establish a reference to make it accessible.

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Frequently Asked Questions

Why does Microsoft Access display an 'Undefined function in expression' error?

This error generally occurs when the function name is spelled incorrectly in your query/macro, the function is declared as Private instead of Public, or the VBA module housing the function shares the exact same name as the function itself.

Can I use a Private VBA function in an Access query?

No, a Private function can only be called by other procedures within the exact same module. To use a custom VBA function in an Access query, form, or macro, it must be declared as a Public function.

How do I fix the 'Compile error: Can't find project or library' message?

This error signifies a missing VBA reference. Open the VBA Editor, navigate to Tools > References, and look for any checked items labeled 'MISSING'. You must uncheck the missing reference or browse to link the correct file path to resolve it.

Excel & Data Problems