Quarterly BAS lodgement is one of the most predictable — and most stressful — events in the Australian small business calendar. The good news: with the right preparation, it takes a fraction of the time and there are far fewer surprises.
Here's the exact process I use with my North Brisbane clients to make every quarter painless.
Know your due dates
The ATO publishes quarterly BAS due dates well in advance. For most small businesses lodging electronically, the standard dates are:
- Q1 (Jul–Sep): 28 October
- Q2 (Oct–Dec): 28 February
- Q3 (Jan–Mar): 28 April
- Q4 (Apr–Jun): 28 July
If you lodge through a registered BAS agent, you usually get a four-week extension. That alone is one of the biggest reasons to engage a bookkeeper — extra time to get it right.
Reconcile every account first
Do not start your BAS until every bank account, credit card, and merchant account is fully reconciled to the last day of the quarter. A BAS prepared on un-reconciled books will almost always have to be amended later.
The reconciliation should match:
- Bank statement closing balance
- Credit card statement closing balance
- PayPal, Stripe, Square or other merchant balances
- Loan account balances against the lender statement
Code GST correctly
The single most common BAS mistake is incorrect GST coding. Watch for:
- Suppliers under the $75k threshold who do not charge GST (no GST claim)
- International purchases (usually GST-free unless GST is shown on the tax invoice)
- Bank fees and merchant fees (input-taxed — no GST)
- Insurance (the stamp duty portion is GST-free)
- Wages and super (BAS-excluded, never GST)
When in doubt, look at the supplier's tax invoice. If GST is not shown, you cannot claim it.
Reconcile payroll for the quarter
Your W1 (gross wages) and W2 (PAYG withheld) figures on the BAS must match your payroll reports for the same quarter. Run your STP YTD report and compare against your draft BAS — they should agree to the cent.
Review before lodging
Before you hit lodge, run a sense check:
- Does total sales (G1) match your P&L revenue for the quarter?
- Is your GST collected vs paid in line with your normal margin?
- Are there any one-off purchases (vehicle, equipment) that need a separate review?
A 10-minute review here catches most errors before they reach the ATO.
Pay on time, even if you cannot pay in full
If cash flow is tight, lodge on time anyway and contact the ATO to set up a payment plan. Late lodgement penalties stack quickly — late payment is far cheaper than late lodgement.
When to hand it off
If BAS preparation is taking you more than a few hours each quarter, or you are constantly amending lodgements, it is time to outsource. A registered BAS agent will handle the mechanics, get you the lodgement extension, and free up the headspace to actually run your business. See my bookkeeping & BAS services or check pricing to get started.