BAS and GST prep (Australia)

What it does

Turns your books into a draft business activity statement (BAS) worksheet using the labels the ATO defines, checks it against your records, lists anything that could move the numbers, and builds a pack for your registered BAS or tax agent. It never lodges or pays anything.

When to use it

• A monthly or quarterly BAS is coming due.
• You ask "how much GST do I owe", "get my BAS ready" or "what goes at G1".
• Straight after au-month-end-close, so the BAS is built on reconciled books.

What you need

• The period, whether you report monthly or quarterly, your GST accounting basis (cash or accruals) and your GST reporting method (Simpler BAS or full reporting). If you don't know, check ATO Online services or ask your agent.
• From your accounting software: the GST or BAS report for the period, profit and loss, a transaction list showing tax codes, bank reconciliation status and a payroll summary (gross wages and tax withheld).
• Your PAYG instalment notice (amount or rate), if you pay instalments.
• Optional connectors: Xero, MYOB or QuickBooks for reports; Google Drive or OneDrive for receipts. Without connectors, upload CSV or Excel exports.

Steps for Claude

1. Confirm the basics. Period, cadence, basis and method; ask, never guess. State the due date from the ATO due dates page, noting agents may have different dates.
2. Books first. Check every bank account is reconciled to the period end, nothing is uncategorised and every transaction has a tax code. If items are open, list them with their likely effect on GST and ask whether to stop or continue with the gap stated as an assumption.
3. GST section.
   • G1 Total sales: GST-free, input-taxed and taxable sales. Under the calculation worksheet method amounts include GST; under the accounts method the owner may report GST-exclusive amounts. Keep one approach and say which.
   • 1A GST on sales and 1B GST on purchases.
   • Full reporting only (GST turnover of $10 million or more): also G2 export sales, G3 other GST-free sales, G10 capital purchases and G11 non-capital purchases.
   • Remove items that don't belong at G1, such as business loans received, private sales, tax refunds and hobby income.
   • Sanity check: for fully taxable sales, 1A should be about one-eleventh of the GST-inclusive amount. Explain any large gap.
   • Flag purchases over $82.50 (including GST) with no tax invoice attached, because the GST credit depends on it.
4. PAYG withholding. W1 total salary, wages and other payments; W2 amounts withheld from W1; W3 other amounts withheld; W4 amounts withheld where no ABN was quoted; W5 = W2 + W3 + W4, copied to label 4. Compare W1 and W2 with the Single Touch Payroll (STP) totals for the period, because the ATO pre-fills these from STP. Flag any difference.
5. PAYG instalments. Option 1: the instalment amount at T7 goes to 5A. Option 2: instalment income (excluding GST) at T1 multiplied by the rate at T2 gives T11, which goes to 5A. Varying an instalment (T3, T4, T8, T9, 5B) is a decision for the owner and their agent; flag it, don't choose.
6. Reconciliation checks. GST control accounts against 1A minus 1B; payroll liability accounts against W2; last BAS actually paid; any known error from an earlier period (point to the ATO page on correcting GST errors and leave the decision to the agent).
7. Build the pack described below.

Output format

Open with: "Draft for review by your registered BAS or tax agent. Not tax advice. Nothing has been lodged."

1. Worksheet table: Label, Amount (AUD), Source report, Note.
2. Checks: each one marked Pass or Flag, with the reason.
3. Open items: what they are and roughly how much they could move the result.
4. Agent pack: the reports to attach, the exceptions list and up to five questions for the agent.

Australian rules and sources (checked 27 September 2026)

• BAS due dates: https://www.ato.gov.au/businesses-and-organisations/preparing-lodging-and-paying/business-activity-statements-bas/due-dates-for-lodging-and-paying-your-bas
• GST reporting methods (Simpler BAS and full reporting): https://www.ato.gov.au/businesses-and-organisations/preparing-lodging-and-paying/business-activity-statements-bas/goods-and-services-tax-gst/gst-reporting-methods
• G1 total sales: https://www.ato.gov.au/businesses-and-organisations/gst-excise-and-indirect-taxes/gst/completing-your-bas-for-gst/complete-your-bas/step-1-sales
• Cash or accruals: https://www.ato.gov.au/businesses-and-organisations/gst-excise-and-indirect-taxes/gst/accounting-for-gst-in-your-business/choosing-an-accounting-method
• Tax invoices: https://www.ato.gov.au/businesses-and-organisations/gst-excise-and-indirect-taxes/gst/tax-invoices
• PAYG withholding labels: https://www.ato.gov.au/businesses-and-organisations/preparing-lodging-and-paying/business-activity-statements-bas/pay-as-you-go-payg-withholding
• PAYG instalment labels: https://www.ato.gov.au/forms-and-instructions/payg-instalments-how-to-complete-your-activity-statement
• STP pre-fill: https://www.ato.gov.au/businesses-and-organisations/hiring-and-paying-your-workers/single-touch-payroll/stp-and-activity-statements
• Correcting GST errors: https://www.ato.gov.au/businesses-and-organisations/gst-excise-and-indirect-taxes/gst/completing-your-bas-for-gst/correcting-gst-errors

Limits

This is not financial or tax advice. Claude does not lodge, pay, vary instalments or estimate penalties. Send anything unusual to your agent, including imports, vehicles, property, mixed supplies, fuel tax credits, fringe benefits and prior-period errors. If the books are not reconciled, the worksheet says so on the first line.

Example requests

• "Here's my Xero BAS report and P&L for July to September. Build the worksheet and tell me what doesn't tie up."
• "I'm on Simpler BAS, cash basis. What goes at G1, 1A and 1B this quarter?"
• "Check my W1 and W2 against my payroll report before I send everything to my BAS agent."