How Auscounts calculates

Plain-language rules behind the GST, BAS and profit and loss figures. Auscounts produces worksheets for you to check. It is not tax, accounting or legal advice, and it does not lodge anything with the ATO for you.

Money is whole cents

Every amount is stored and added up as a whole number of cents. Dollars and cents are only shown on screen. We never add up decimal dollar amounts, so there is no floating-point drift.

GST

• Rate. GST is 10% of the price before GST. When you type a price that already includes GST, the GST in it is one eleventh of that price.
• Rounding. The GST on each line is rounded to the nearest cent, with half a cent rounded away from zero, and then the lines are added up. The ATO lets a business round either per line (the taxable supply rule) or once on the invoice total (the total invoice rule); Auscounts uses per line. Example: two lines of 5 cents before GST give 1 cent of GST each, 2 cents in total, where the invoice total rule would give 1 cent.
• Credits and refunds. A negative line gets exactly minus the GST of the same positive line, so a credit for a line reverses the GST that line charged. A 5 cent credit line gives minus 1 cent, not zero. The ATO text does not spell out how to round a negative half cent; this is our decision, made so that a credit cancels its sale.
• GST-free and input-taxed. A line only carries GST when its GST box is ticked. Each journal line also carries a tax code: GST, GST-free, input taxed, no GST or capital purchase. On an invoice, bill or bank line the code comes from that line's GST box and the account: GST ticked is GST, GST unticked on a taxable account is GST-free, and an input-taxed or no-GST account keeps its own treatment. On a manual journal you can pick the code for each line; if you leave it on Account default it takes the account's GST setting. GST-free sales go in G1 and G3, input-taxed sales go in G1 only, and neither has GST. Input-taxed sales carry no GST credit for related purchases.
• Older entries. Journal lines posted before tax codes were added have no code stored. For those the BAS falls back to the account's GST setting, as it did before.

Cash or accrual

You choose cash or accrual in Setup (accrual needs a paid plan).

• Accrual. Sales, purchases and their GST are reported in the period of the invoice or bill date.
• Cash. The ATO reports sales and purchases in the period you are paid or pay. Auscounts holds the GST on an invoice or bill in a pending account until the payment is made, then moves the part covered by the payment into GST collected or GST paid. So 1A and 1B follow the payment date on cash basis.
• G1, G3, G10 and G11 on cash basis. These also follow the payment date. Each payment is split into its GST and its amount before GST, and the amount before GST is shared across the lines of the invoice or bill in proportion to each line's share of the document. A part payment therefore reports a part of each line, and the last payment takes whatever is left so a fully paid document reports exactly its total. An unpaid invoice or bill is not reported at all on cash basis. This split is our reading of the ATO's cash basis rule; the ATO pages do not give a worked example of a part-paid invoice with several lines.
• Changing basis. A document keeps the basis it was authorised under: documents authorised with GST held as pending stay on cash timing, and documents authorised with GST collected straight away stay on invoice-date timing. A document with no GST follows the basis set in Setup. We have not built the ATO's transitional rules for switching basis.
• Profit and loss. Profit and loss follows the document date on both bases.

What each BAS label means and where it comes from

Each label is added up from the journal lines dated inside the BAS period, in full cents. The cents are then dropped once on the total (truncated, never rounded up), because the ATO asks for whole dollars. Net GST and the totals below use the whole-dollar labels, not the cent amounts.

Label	What it is	Where Auscounts gets it
G1	Total sales including GST	Income accounts (taxable, GST-free and input-taxed) plus GST collected
G3	GST-free sales	Income lines whose tax code is GST-free
G10	Capital purchases including GST	Lines coded as capital purchases (a bill or bank line coded to an asset account you created, or a manual journal line with the capital choice), plus the GST on them
1A	GST on sales	The GST collected account
G11	Non-capital purchases including GST	Every purchases and expense account, whatever its code, plus GST paid, less anything counted at G10
1B	GST credits on purchases	The GST paid account
5A, 5B	PAYG instalment and variation credit	Typed in by you for the period
8A, 8B, 9	Totals on the activity statement	8A = 1A + 5A. 8B = 1B + 5B. 9 = 8A − 8B: a payment if positive, a refund if negative

The Mark BAS submitted journals and reversed entries are left out of every label. When you mark a period submitted, the amounts, the Auscounts version and the GST rules version are saved with it, and those saved amounts do not change if rules change later.

Capital purchases and the $1,000 rule. The ATO says that if you record capital and non-capital purchases separately you use that breakdown at G10 and G11. If you do not, and you expect GST turnover under $1 million, capital items costing more than $1,000 go to G10 and the rest can go to G11. Auscounts lets you tag capital lines, so everything you tag goes to G10 whatever its price. We do not apply the $1,000 shortcut, and we could not confirm from the ATO page whether the $1,000 includes GST, so it is recorded in our rules table as a GST-inclusive figure that is not yet used.

Simpler BAS. The ATO says most businesses with GST turnover under $10 million use Simpler BAS, where only G1, 1A and 1B are reported. G3, G10 and G11 are shown here as worksheet figures; you may not need to enter them.

Labels Auscounts does not produce: G2 (exports), adjustments (credit notes, bad debts, change of business use), private-use splits, PAYG withholding (W1 to W5, label 4), label 7 and the other less common labels. Use the ATO forms for those.

Profit and loss

• Income, minus cost of goods sold (accounts coded 5xxx, type purchases), is gross profit.
• Gross profit minus expenses (6xxx) is profit.
• All amounts are before GST, taken from journals dated inside the report period.

How we test the arithmetic

We keep a set of test cases taken from ATO worked examples and rules. Each one lists where the numbers came from and which numbers are ours. The checks are arithmetic based on our interpretation of ATO formulas. No accountant or registered BAS agent has reviewed them or signed them off, and the ATO has not endorsed them. Profit and loss expectations are derived by us (the ATO does not publish them) and are labelled derived.

The rules-only cases (rounding, truncation, 8A, 8B, 9 and period boundaries) run automatically before every release and stop it if any fails. The cases that post real invoices, bills and payments run against a database on a developer machine.

Where a case shows Auscounts differs from the ATO material, we keep the case, mark it as a known gap, and do not claim it. Current state, generated from the test files:

The version number

Auscounts versions look like Year.Month.PRsThisMonth, for example 1.10.23. Year counts from 2025 (2026 is 1, 2027 is 2), Month is the calendar month in Brisbane, and the last number counts the changes released so far that month. It is shown in the footer inside the app and saved with each BAS you mark as submitted, so you can tell which version produced a figure.

Worksheets, not advice

Everything in Auscounts is a worksheet for you, your accountant or your BAS agent to check before anything is lodged. You are responsible for what you lodge. If something here looks wrong, tell us at info@auscounts.com.