For many small business owners, lodging a Business Activity Statement (BAS) can feel like just another compliance task on an already long to-do list. However, even small mistakes can lead to unnecessary stress, cash flow issues, penalties or unwanted attention from the Australian Taxation Office (ATO).

Here are some of the most common BAS mistakes we see and how you can avoid them.

1. Mixing Personal and Business Expenses

One of the biggest mistakes business owners make is using the same bank account for both personal and business transactions.

This can create confusion, make bookkeeping more difficult and increase the risk of claiming expenses that are not business related.

How to avoid it:

• Maintain separate business and personal bank accounts.
• Use a dedicated business credit card where possible.
• Reimburse yourself correctly rather than paying personal expenses directly from the business account.

2. Claiming GST Without a Valid Tax Invoice

To claim GST credits, you need appropriate documentation. Many business owners assume a bank transaction or receipt is enough, but this is not always the case.

How to avoid it:

• Keep copies of all tax invoices.
• Use cloud accounting software to store digital records.
• Check that supplier invoices include GST before claiming a credit.

3. Reporting the Wrong GST Amount

GST coding errors are common, particularly when transactions are entered manually. Some expenses are GST-free, while others include GST, and getting these mixed up can affect your BAS.

How to avoid it:

• Review your GST settings regularly.
• Ensure your accounting software is configured correctly.
• Seek professional advice when unsure about GST treatment.

4. Missing BAS Deadlines

Late lodgement can result in penalties and interest charges, even if you cannot pay the amount owing immediately.

How to avoid it:

• Set calendar reminders before each due date.
• Lodge on time, even if payment arrangements need to be made later.
• Work with a registered BAS or tax agent who can help manage deadlines.

5. Forgetting to Include All Income

Some businesses accidentally omit income from cash sales, online platforms or secondary revenue streams. The ATO receives information from many sources and discrepancies can trigger further review.

How to avoid it:

• Reconcile bank accounts regularly.
• Ensure all sales channels are captured in your accounting system.
• Review reports before lodging your BAS.

6. Not Reconciling Accounts Before Lodgement

Submitting your BAS without reconciling bank accounts can result in inaccurate reporting and missed transactions.

How to avoid it:

• Reconcile bank accounts monthly.
• Check for duplicate transactions.
• Investigate unusual balances before lodging.

7. Ignoring PAYG and Super Obligations

Many business owners focus solely on GST and overlook employee obligations such as PAYG withholding and superannuation.

How to avoid it:

• Ensure payroll software is up to date.
• Verify PAYG withholding amounts each quarter.
• Pay superannuation on time to avoid penalties.

8. Waiting Until the Last Minute

Leaving your BAS preparation until the due date often leads to rushed decisions, overlooked transactions and costly mistakes.

How to avoid it:

• Keep your bookkeeping current throughout the quarter.
• Schedule regular reviews of your financial records.
• Address issues early rather than scrambling at lodgement time.

9. Not Seeking Professional Advice

Many BAS mistakes occur because business owners try to navigate complex tax requirements on their own.

How to avoid it:

• Work with an accountant or BAS agent who understands your industry.
• Ask questions before lodging if you’re unsure.
• Use professional advice to identify opportunities and avoid costly errors.

Overview

Your BAS is more than just a compliance obligation. When prepared correctly, it provides valuable insights into your business performance and helps you stay on top of your tax obligations.

By maintaining accurate records, keeping your bookkeeping up to date and seeking professional guidance when needed, you can avoid common BAS mistakes and gain greater confidence in your business finances.

Need help with your BAS?

At Tri Accounting, we help small business owners stay compliant while gaining a better understanding of their financial position. Whether you need assistance with BAS preparation, bookkeeping or business advisory services, our team is here to help.

Book your free consultation today and let us take the stress out of BAS lodgements.