Every Australian business registered for GST must lodge a Business Activity Statement (BAS) with the ATO — either monthly, quarterly, or annually depending on your turnover and reporting obligations.
Most small businesses lodge quarterly. The due dates are 28 October, 28 February, 28 April, and 28 July (or 28 August if you lodge through a registered tax agent). Late lodgement attracts a Failure to Lodge (FTL) penalty of one penalty unit for each 28-day period the BAS remains outstanding.
Your BAS reports GST collected on sales, GST credits on purchases, PAYG withholding from employee wages, and PAYG income tax instalments. The ATO's online portal and most accounting software (Xero, MYOB, QuickBooks) can pre-fill much of this — but you still need to reconcile bank transactions and verify the figures before submitting.
Common mistakes include claiming GST credits on BAS-exempt items (like basic food, some medical services, and input-taxed financial supplies), misreporting private expenses as business deductions, and failing to account for the GST on mixed-use assets. An error on your BAS can trigger an ATO review or audit.