The due dates
For quarterly lodgers — which is most small trade businesses:
| Quarter | Period | Due |
|---|---|---|
| Q1 | July – September | 28 October |
| Q2 | October – December | 28 February |
| Q3 | January – March | 28 April |
| Q4 | April – June | 28 July |
Q2 gets the extra month because of the Christmas shutdown. If you lodge monthly, the statement is generally due on the 21st of the following month. Lodging through a registered BAS or tax agent can earn you a later date under the ATO's agent lodgment program.
Before you start: know your basis
Cash or accruals decides which quarter a sale lands in. On a cash basis you account for GST when the money actually moves; on an accruals basis when the invoice is issued. An invoice raised on 29 June and paid on 3 July falls in different quarters depending on which one you are on. Check before reconciling, not after.
The quarterly checklist
1. Sales
- Every job completed in the quarter has an invoice raised against it
- No gaps or duplicates in the invoice numbering
- Each invoice shows the correct GST treatment per line — taxable versus GST-free
- Payments received are recorded against the right invoice, including part payments and stages
- Credit notes and refunds are captured, not just deleted invoices
2. Purchases
- You hold a valid tax invoice for every purchase over $82.50 including GST you intend to claim
- Supplier invoices actually show an ABN and a GST amount — no ABN means no credit, and possibly a withholding obligation
- GST-free purchases are not sitting in the claimable pile
- Private-use portions are apportioned, not claimed in full
- Vehicle, tool and phone expenses are split the way your accountant set them up
3. Reconcile
- Bank account matches your records for the whole period, not just the closing balance
- Total GST collected equals one eleventh of your taxable sales (a fast sanity check)
- Cash jobs are in the system — this is the single most common omission
- Any deposits held that have not yet been invoiced are treated correctly for your basis
4. Other labels
- PAYG withholding, if you have employees
- PAYG instalments, if the ATO has you on them
- Fuel tax credits, if you are eligible
Where the numbers usually go wrong
| Problem | Cause | Fix |
|---|---|---|
| GST collected does not equal 1/11 of sales | GST-free lines mixed into taxable totals | Apply GST per line item, not to the invoice total |
| Totals a few cents out | Rounding on running totals in a spreadsheet | Hold amounts in whole cents; round once, per line |
| Missing income | Cash jobs never invoiced | Raise an invoice for every job, however it was paid |
| Credits disallowed | Supplier document is not a valid tax invoice | Ask for a compliant one before you pay it |
| Quarter boundaries wrong | Cash and accruals treatment mixed | Pick the basis you are registered for and apply it consistently |
Lodge on time even if you cannot pay
Late lodgment and late payment are two separate problems with two separate consequences. Lodging on time and then arranging a payment plan is a considerably better position than not lodging at all — and it is the one thing on this page that is entirely within your control at the deadline.
Make next quarter easier
Everything in the checklist above is a record you either kept as you went or have to reconstruct. Invoices raised the day work finishes, payments recorded when they land, and GST applied per line item at the time — that is the whole trick. See what has to be on a tax invoice and how to calculate GST for the two details that cause most of the quarter-end rework.
Source
Due dates come from the ATO's due dates for lodging and paying your BAS. General information only, not tax advice — your accountant or registered BAS agent should confirm how this applies to you.