Free online ACCDB to MDB converter

Older Access applications, database connectors, and devices may accept only the MDB format, while Access 2007 and later normally create ACCDB files. Converting provides a compatible copy for legacy software or users who cannot open newer Access databases.

What the ACCDB format is

ACCDB is the default Microsoft Access database format introduced with Access 2007. Desktop versions of Access included with supported Microsoft 365 plans and standalone Office releases can create ACCDB files containing tables, queries, forms, reports, macros, relationships, indexes, and VBA modules.

ACCDB supports features unavailable or incompatible in older MDB databases, including attachment fields, multivalued fields, calculated fields, and newer encryption methods. It uses the ACE database engine rather than the older Jet engine associated with classic MDB files.

What the MDB format is

MDB is the database format used by Access 2000 and Access 2002–2003, although earlier Access releases also used compatible MDB variants. It remains useful with legacy Access applications, older ODBC or OLE DB connections, and software designed for the Jet database engine.

MDB can store tables, queries, forms, reports, macros, relationships, and VBA modules, but it cannot represent every ACCDB feature. An MDB database has a 2 GB maximum file size, including internal objects and data. MDB also uses older security and encryption capabilities; Access 2007 and later do not support the former Access user-level security model in ACCDB databases.

How to convert the database in Microsoft Access

1. Make a backup copy of the original .accdb file and open the copy in Access 2007 or later. Close other applications and users that have the database open.
2. Review the database for attachment fields, multivalued fields, calculated fields, newer encryption, and other Access-specific features that the MDB format cannot store.
3. Choose File → Save As → Access 2002–2003 Database (*.mdb). If the receiving application requires Access 2000 compatibility and that option is available, choose Access 2000 Database (*.mdb) instead.
4. Enter an output filename ending in .mdb, select a destination, and choose Save. Access creates an MDB copy; the ACCDB source remains unchanged.
5. Open the new MDB in the intended legacy application and test its tables, queries, forms, reports, macros, relationships, VBA code, permissions, and linked data sources.

If Access rejects the conversion because of incompatible objects, create a blank database, save it in the required MDB format, and use External Data → New Data Source → From Database → Access to import compatible tables and other objects. Recreate unsupported fields, expressions, forms, reports, and queries manually, then relink external tables.

Converting without installed desktop software

You can convert the file on 101convert.com for free without installing software: upload the ACCDB file, select MDB as the output format, start the conversion, and download the result. Do not upload confidential or regulated data unless the service’s storage, processing, and deletion terms meet your requirements. Verify which database objects the resulting file contains; a converter may preserve data without preserving every form, report, macro, relationship, or VBA module.

Compatibility and quality checks

Conversion is not guaranteed to be lossless. Attachment fields, multivalued fields, calculated fields, newer encryption settings, and other ACCDB-only objects may be rejected, flattened, or require redesign. Databases built from conventional tables, relationships, queries, forms, reports, and compatible VBA have a better chance of converting intact.

After conversion, check field types and properties, indexes, relationships, query expressions, broken references, VBA compatibility, linked tables, external data paths, forms, reports, and startup behavior. Older Access versions may require replacement functions or updated VBA references.

If the source or required output exceeds 2 GB, one MDB file is not suitable. Split the database into a front end containing forms, queries, and code and one or more back-end MDB files, or keep the database in ACCDB format.

Running Database Tools → Compact and Repair Database on a backup copy before conversion can correct structural errors and reduce unnecessary size, but it does not make unsupported ACCDB features compatible with MDB.