MDB vs ACCDB: What Is the Difference?

The short version

MDB is the older Access database format used by Access 97 through Access 2003. ACCDB is the newer format introduced with Access 2007 and still used by Microsoft 365 Access.

For simple table viewing and CSV export, the practical difference is usually small. For editing, encryption, attachments, calculated fields, and application features, the difference matters much more.

Format comparison

• MDB uses the Jet database engine; ACCDB uses the newer ACE engine.
• Both formats have a 2 GB file size limit.
• ACCDB supports attachment fields, multi-value fields, calculated fields, and stronger encryption.
• MDB is often easier to process with older open-source tools.
• ACCDB is more common in databases created after 2007.

Compatibility risks

A viewer can usually read stored table data, but it cannot reproduce a full Access application. Forms, reports, macros, VBA modules, custom menus, and linked tables depend on Microsoft Access itself.

If you are migrating data, treat the Access file as two things: tables that can be exported, and application logic that must be documented or rebuilt separately.

Which one should you convert first?

• Convert MDB first when you are dealing with older public datasets or legacy business archives.
• Convert ACCDB first when the database was created after 2007 or uses modern Access field types.
• Keep the original file until the migration has been checked table by table.
• Export related tables together so foreign keys can be rebuilt later.