The quickest way to get a BAS wrong is to divide your total expenses by eleven.
It is an understandable shortcut. GST is 10%, so the GST component of a GST-inclusive price is one-eleventh of it, and for a lot of transactions that arithmetic is exactly right. The problem is the transactions where it is not — and in a typical small business that is a meaningful share of spending.
Bank fees. Most fresh food. Residential rent. Payments to suppliers who are not registered for GST. Overseas software subscriptions, depending on the supplier. In each case the GST component is nil, and treating them as one-eleventh overstates your credits.
A sheet that handles this well does not do anything clever. It just records the GST treatment per transaction, at the time, with the evidence attached.
The columns that make a BAS
| Column | Example | Notes |
|---|---|---|
| Date | 2026-07-18 | Transaction date |
| Supplier | Bunnings | As printed |
| Supplier ABN | 11 005 357 522 | From the tax invoice |
| Description | Timber and fixings, Kemp St job | What, and for what |
| Total (inc GST) | 341.00 | What you actually paid |
| GST amount | 31.00 | From the invoice, not calculated |
| GST treatment | Taxable | Taxable / GST-free / Input taxed / No ABN |
| Category | Materials | Your own expense category |
| Tax invoice held | Yes | The claim depends on this |
| Receipt URL | link | The evidence |
Two of these columns do the work that the one-eleventh shortcut skips.
GST amount comes from the invoice. A valid tax invoice states the GST, and that stated figure is what you claim. Where an invoice covers a mix of taxable and GST-free items — a supermarket run with both fresh produce and cleaning products is the everyday example — the GST will not be one-eleventh of the total, and the invoice will say so.
GST treatment explains the amount. A zero in the GST column with no explanation is indistinguishable from an oversight. "GST-free" or "No ABN" turns a blank into a decision.
The treatments worth knowing
Taxable. The normal case. GST included, credit claimable if you hold a valid tax invoice and the purchase relates to your business.
GST-free. No GST was charged and none is claimable. Most basic food, most health and medical, some education, and certain exports. The practical trap is the mixed shop: a café owner buying milk and bread (GST-free) alongside detergent and paper cups (taxable) on one docket.
Input taxed. Mainly financial supplies and residential rent. No GST charged, no credit available. Most bank fees sit here, which is why "bank fees divided by eleven" is a recurring error.
Supplier not registered. A small supplier under the registration threshold cannot charge GST and their document is not a tax invoice. Legitimate transaction, no credit. This is the one most likely to be misclaimed, because the paperwork can look similar at a glance.
The quick check: a valid tax invoice shows the supplier's ABN and either states the GST amount or states that the total includes GST. If neither appears, pause before claiming.
Tax invoice thresholds
For lower-value purchases the documentation requirements are lighter, and above a threshold the invoice has to include more — including, for higher-value purchases, the buyer's identity. The threshold figures are set by the ATO and are worth confirming against current guidance rather than memory, because they have moved over time.
What matters for your sheet design is the "tax invoice held" column. At BAS time you are asserting that you hold valid documentation for the credits you are claiming. A column that says yes or no, backed by a linked image, makes that assertion checkable in seconds instead of being an act of faith.
A worked quarter
A small café, July to September, simplified:
| Treatment | Transactions | Total spent | GST claimable |
|---|---|---|---|
| Taxable | 94 | 38,420 | 3,492 |
| GST-free | 61 | 14,780 | 0 |
| Input taxed | 12 | 410 | 0 |
| Supplier not registered | 7 | 2,240 | 0 |
Total spending is $55,850. One-eleventh of that is $5,077. The actual claimable GST is $3,492 — a $1,585 difference across a single quarter, almost all of it from GST-free food purchases.
Note also that the taxable GST figure is $3,492 rather than exactly one-eleventh of $38,420 ($3,493). That one-dollar gap is rounding across ninety-four invoices, and it is why the GST column should hold invoice figures rather than formula output. The formula is close. Close is not what you report.
Getting the numbers out
With the treatment column in place, your BAS inputs are a pivot table: GST treatment down the rows, sum of GST amount and sum of total across the columns. One click gives you the claimable total and a breakdown you can defend.
Three formulas worth having on a summary tab:
=SUMIF(Treatment,"Taxable",GST_Amount)— your claimable GST=SUMIF(InvoiceHeld,"No",GST_Amount)— GST you are claiming without documentation, which should be zero=COUNTIF(Treatment,"")— unclassified rows, which should also be zero before you lodge
That second one is a genuine control. Run it before every lodgement.
Keeping it current through the quarter
The treatment column is only reliable if it is filled in when the transaction is fresh, because it depends on reading the invoice. Three months later, with the docket faded, the honest answer becomes a guess.
Capture on the day: Scan2Sheet pulls the supplier, date, total, and the tax component off the invoice image and lands the row in the sheet with the image linked, which leaves you the treatment dropdown and the description. For a tradie or café owner that is a few seconds at the counter rather than an evening at the end of the quarter.
Before you lodge
- No blank GST treatments
- No claimed GST on rows marked "tax invoice held: No"
- GST-free total is plausible for your business — if a café shows almost no GST-free spending, something is misclassified
- Supplier ABNs present for the larger purchases
- Spot-check five rows against their linked images
Set the sheet up this way at the start of a quarter rather than mid-way. A quarter with consistent treatments beats a quarter you have to re-read invoice by invoice.