How to Prepare BAS: A Simple Guide for Australian Businesses

BAS time often becomes stressful for Australian businesses because small gaps in record-keeping or unclear GST treatment can throw the whole statement off. The pressure builds quickly when transactions pile up, and the filing deadline approaches, making the task feel bigger than it is. A steady process and the right checks can make BAS preparation far more manageable and reduce the usual rush.

In this blog, we will explain the process of preparing BAS and the important checklist to keep in mind.

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How to Prepare BAS?

Australian businesses prepare their BAS by first gathering and reconciling financial records, classifying transactions, and calculating the relevant tax components. Once the numbers are accurate, they generate and review their BAS reports, lodge the statement, and make the required payment. For a better understanding of BAS preparation, see the steps below:

1. Gather and Reconcile Financial Records

• Confirm BAS Lodgment Period (monthly, quarterly or annually). Businesses with over $20m turnover lodge monthly, under $20m voluntarily lodge quarterly, and registered small operators may lodge annually).
• Collect sales records and all issued tax invoices.
• Gather purchase bills and supplier tax invoices.
• Download bank, credit card, and loan statements for the BAS period.
• Compile payroll details, including gross wages and PAYG withholdings.
• Record petty cash activity and other cash transactions.
• List any capital asset purchases such as equipment or vehicles.
• Reconcile all bank and credit card accounts to ensure every transaction is accurately recorded.

2. Classify Transactions and Calculate Tax Components

• Apply correct GST codes to each transaction (GST Free, BAS Excluded, GST on income).
• Calculate GST on sales (G1), which is the GST collected from customers.
• Calculate GST credits (G10 and G11) on eligible business purchases.
• Verify the PAYG figures, including W1 (total wages paid) and W2 (tax withheld), to ensure they are accurate.
• Review your PAYG instalments that appear pre-filled by the ATO.
• Include any additional applicable taxes, such as fuel tax credits, Luxury Car Tax, or Wine Equalisation Tax (WET).

3. Generate, Review, and Validate BAS Figures

• Run the Activity Statement Report in your accounting software, or total the figures manually if preparing without software.
• Recheck all figures for accuracy or unusual variances compared to previous periods.
• As part of validating the data, make sure the final figures align with prior periods where applicable and round them to whole dollars before lodging.

4. Lodge the BAS

• Lodge BAS through the ATO Business Portal or provide it to your registered BAS expert or tax agent.
• Submit your BAS by the due date, even if it is a nil return.
• Keep the lodged BAS and supporting documents for at least five years.

5. Make Payment or Receive Refund

• If you owe BAS, pay it by these ATO deadlines:
• Monthly BAS: 21st of the following month
• Quarterly BAS:
  • Q1 (Jul–Sep): 28 Oct
  • Q2 (Oct–Dec): 28 Feb
  • Q3 (Jan–Mar): 28 Apr
  • Q4 (Apr–Jun): 28 Jul
• Annual BAS: 31 October (or the date of your tax return if lodged through an agent).

• If you are due for a refund, the ATO will deposit the amount into your nominated bank account.

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Important Checklist to Follow While Preparing for BAS

Before diving into the details, it helps to get clear on what a solid BAS prep routine should cover.

Your goal is simple: clean data, accurate reconciliations, and figures that genuinely reflect your activity for the period. A quick upfront review ensures your GST claims are correct, your payroll numbers line up, and no adjustments or obligations slip past you.
Below is the detailed checklist to guide you through each step.

• Double-check the BAS reporting period and lodge-by date, so you’re working within the correct timeframe.
• Reconcile every bank, sales, and purchase account to ensure no missing or duplicated transactions slip through.
• Verify all invoices and receipts so GST claims are fully supported and compliant.
• Record any GST adjustments accurately, especially for bad debts, discounts, or private-use corrections.
• Cross-check the PAYG figures (W1 and W2) with your STP finalisation or payroll reports to confirm they match.
• Review your PAYG instalment figures (T1–T4) to avoid overpayment or underpayment.
• Add Fuel Tax Credits if you meet the eligibility criteria and have proper usage records.
• Include any additional obligations such as FBT, LCT, or WET where applicable to your business.
• Lodge and pay your BAS on time to avoid penalties and interest charges.

Bring in a BAS Professional and Remove the Stress from Compliance

Your business may be in an early stage, mid-stage, or mature. No matter where you stand, you already know how important it is to prepare BAS with strong compliance knowledge and an understanding of business-related deductions. While proper checklists and internal procedures help, there is another strategy worth considering: outsourcing.

The rise of professional services for bookkeeping outsourcing gained popularity mainly for cost benefits, but it has also become a dependable way for businesses to gain specialised expertise, stay updated with the latest accounting trends, and maintain alignment with ATO requirements.

Whiz Consulting is a trusted bookkeeping outsourcing services provider for businesses across Australia. We support not only basic bookkeeping but also payroll, financial reporting, and more, with full adherence to ATO guidelines. Our accountants assist you in preparing your BAS with every key aspect in place. Connect with us today and let us handle the workload so you can focus on scaling your business confidently.