I've been using Quickbooks desktop 2011/2012 to run two entities, i.e. my small one-man business and also my SMSF. Can I do this with my Quickbooks online subscription?

Thanks for posting here in the Community, scott-nulinkanal. 

If you have multiple companies with different ABN and need to lodge BAS separately, you'll need to have a different subscription for each company. One QuickBooks Online subscription is for one company file and can only assign one ABN on each subscription. 

However, if your business has multiple departments or locations, you can consider using the class and location tracking function. This feature is available in QuickBooks Online Plus which helps you track the ins and outs for each department or location.

You can also contact our live support Team  if you need any help with choosing a QuickBooks Online plan that suits on your business needs. 

Feel free to post again if you need further assistance with QuickBooks Online. Have a great day!