Free Australian business tool
BAS quarter GST estimator
Work out roughly what this quarter's GST bill looks like before it arrives — GST collected on sales, GST credits on purchases, and the net figure, with the lodgement date attached.
- GST on sales and GST credits, both halves
- Quarterly due dates, weekend-adjusted
- How much to set aside per $100 invoiced
Docketlane is a drafting tool, not tax or legal advice.
The number that ruins a quarter
GST does not feel like the ATO's money while it is in your account. It arrives with every payment, sits alongside everything else, and gets spent on materials, fuel and the mortgage. Then the 28th comes around and the bill is for money that was already used.
The fix is not discipline, it is arithmetic done early. If you know roughly what the quarter owes by week two, you can put it aside as it comes in instead of finding it at the end. That is all this estimator is for.
The rule of thumb worth carrying: on a GST-inclusive invoice, about $9.09 of every $100 is GST — one eleventh. What you actually hand over is less, because the GST inside your business purchases comes back off.
Both halves of the calculation
A quarterly BAS for a small business is simpler than its reputation. Under Simpler BAS, businesses with a GST turnover under A$10 million report three things: total sales, the GST on sales, and the GST on purchases. Everything else on the form belongs to bigger or more complicated businesses.
| Label | What goes in it |
|---|---|
| G1 | Total sales for the quarter, GST included |
| 1A | GST you collected on those sales |
| 1B | GST you paid on business purchases, claimed back as credits |
| 1A − 1B | What you pay — or, if it is negative, what you are refunded |
The half most sole traders under-claim is 1B. Every business purchase that carried GST and that you hold a tax invoice for reduces the bill: tools, materials, fuel, insurance, phone, software, the accountant. Missing them does not save time, it just donates money.
Only the business share counts. A phone used half for work claims half the GST, and a receipt you cannot produce is a credit you cannot support if the claim is ever examined.
When each quarter is due
| Quarter | Period | Due |
|---|---|---|
| 1 | July – September | 28 October |
| 2 | October – December | 28 February |
| 3 | January – March | 28 April |
| 4 | April – June | 28 July |
The December quarter gets an extra month because of the Christmas shutdown. If the 28th lands on a weekend or public holiday, the next business day applies — this tool adjusts for weekends, but public holidays vary by state and are not applied.
Lodging through a registered tax or BAS agent can extend some of these dates, and lodging online sometimes attracts a concession. Businesses over A$20 million turnover report monthly, and some small businesses report annually.
Lodge even when you cannot pay in full. Lodging on time and arranging a payment plan is a very different position from not lodging at all.
Making the next quarter easier than this one
- Move the GST out as it arrives. A second account that only ever receives the GST portion turns the 28th into a transfer.
- Record expenses when they happen, not in a panic at the end. The credits you cannot find are the ones that cost you.
- Keep the tax invoices, not just the bank line. A statement entry is not evidence of GST paid.
- Reconcile against your invoices, not your memory. Cash-basis and accruals-basis reporting count a payment at different moments, and guessing at the difference is how errors start.
Docketlane's BAS report does this from your own records: GST on the invoices you issued and GST on the expenses you recorded, totalled for the quarter you choose. The estimator above is the version for anyone who has not put their records anywhere yet.
This page explains general GST reporting concepts and produces an estimate. It is not tax advice, it does not lodge anything, and it is not connected with or endorsed by the ATO. For your own circumstances, the ATO's guidance and a registered tax or BAS agent are the right sources.
Common questions
- How much GST will I owe this quarter?
- Roughly one eleventh of your GST-inclusive sales, less one eleventh of your GST-inclusive business purchases. On $44,000 of sales and $11,000 of purchases that is $4,000 collected minus $1,000 in credits, so about $3,000 payable.
- When is my BAS due?
- For standard quarterly reporting: 28 October, 28 February, 28 April and 28 July, covering the quarters ending September, December, March and June. The December quarter gets the extra time because of Christmas.
- What if my GST credits are more than the GST I collected?
- You are due a refund rather than a payment. That is common in a quarter with a large equipment purchase or a lot of stock bought ahead of the work.
- Do I have to lodge a BAS if I made no sales?
- If you are registered for GST and required to lodge for the period, yes — a nil statement still has to be lodged. Not lodging is treated differently from lodging nothing owed.
- Does this replace my BAS?
- No. It estimates the GST portion so you can set money aside and sanity-check what you are lodging. The actual statement may include PAYG instalments, PAYG withholding and other labels this does not model.
- Cash or accruals — does it change the answer?
- It can. Cash-basis reporting counts GST when money moves; accruals counts it when the invoice is issued. Around quarter boundaries the two can differ noticeably, so use the totals that match the method you report on.