Debt Analyzer utilizes an optional automated backup feature. Click on Options | Preferences | Backup from the program's main window to set the schedule or turn off the automatic backups. The backup file is saved to the location selected in the Backup preference panel.
When closing Debt Analyzer the above dialog opens, prompting to continue with the backup. Click Yes to back up the file or No to close the program without backing up.
If not using the automated backups, open the main window and click on File | Back Up Debt Plan to create a backup when necessary. Use the File | Restore Debt Plan menu option to restore from a backup.