It’s 10:47 pm. You’re halfway through tomorrow’s client proposals when you remember the BAS is due.

Then the questions start:

Have all the bank transactions been reconciled? Where is that missing receipt? Why does GST collected look higher than expected? And why does Xero show a different figure from the spreadsheet you prepared last month?

If that sounds familiar, you’re not alone. Many Australian business owners only think about their BAS when the deadline is breathing down their neck.

The good news? Your 2026–27 BAS calendar is predictable once you understand the rhythm. There is one important exception, though : and it catches plenty of businesses out every year.

What are the 2026–27 quarterly BAS due dates?

If your business reports GST quarterly, each BAS covers a three-month period.

For most quarters, the standard self-lodgement date is the 28th day of the month following the quarter. However, eligible online lodgers and businesses working with a registered BAS or tax agent may receive additional time for Quarters 1, 3 and 4.

Here’s the calendar at a glance:

BAS quarter	Period covered	Standard due date	Online self-lodgement date*	BAS or tax agent date*
Q1	1 July–30 September 2026	28 October 2026	11 November 2026	Approximately 25 November 2026
Q2	1 October–31 December 2026	28 February 2027	Monday 1 March 2027	Monday 1 March 2027
Q3	1 January–31 March 2027	28 April 2027	12 May 2027	Approximately 26 May 2027
Q4	1 April–30 June 2027	28 July 2027	11 August 2027	Approximately 25 August 2027

*Online and agent dates apply only where the relevant concession is available and eligibility requirements are met. Always confirm your specific due date through the ATO’s BAS due-date guidance or with your registered agent.

The dates are easier to remember as a pattern:

Q1: October, then possible extensions in November
Q2: February, with no additional concession
Q3: April, then possible extensions in May
Q4: July, then possible extensions in August

Simple enough, right? Mostly.

Why is Q2 the BAS deadline that catches everyone?

Quarter 2 covers 1 October to 31 December 2026.

Its statutory due date is 28 February 2027. But in 2026–27, 28 February falls on a Sunday. That means the practical due date moves to the next business day:

Monday, 1 March 2027

This applies to everyone reporting quarterly GST:

Businesses lodging their own BAS
Businesses lodging online
Businesses using a registered BAS agent
Businesses using a registered tax agent

There is no additional two-week online concession for Q2 and no further BAS agent concession for this quarter.

Why? The Q2 due date already includes the longer February timing. So while Quarters 1, 3 and 4 may give you a little extra breathing room, Q2 does not.

This is the one to put in your calendar now. Don’t assume your agent automatically has another month up their sleeve. They don’t for this quarter.

For the most authoritative detail, see the ATO BAS agent lodgment program for 2026–27.

What are the BAS extensions for online lodgement?

Quarterly GST reporters who lodge online may receive an automatic two-week extension for:

Quarter 1
Quarter 3
Quarter 4

That means you may have extra time to lodge and pay, provided you meet the requirements for the concession.

However, the extension does not apply to Q2.

Think of it like a train timetable. Most services run on the same predictable route, but Q2 takes a different track. If you use the usual timetable without checking, you could arrive at the station a day late : and the ATO is not famous for accepting “I thought it was next month” as a strategy.

Can a BAS agent give you more time?

Working with a registered BAS or tax agent may provide a further concession for Quarters 1, 3 and 4. In practical terms, this is generally around four weeks after the standard due date, subject to the relevant ATO program and your circumstances.

For 2026–27, the approximate agent dates are:

Q1: 25 November 2026
Q3: 26 May 2027
Q4: 25 August 2027

There is no agent concession for Q2. The effective deadline remains Monday, 1 March 2027.

It’s also important to remember that an extension is not a reason to leave everything until the final week. It is a safety net, not a business process.

The more useful approach is to prepare your file as though the standard date applies, then treat the extension as breathing space for unexpected issues.

What actually causes a BAS to be lodged late?

The deadline itself is rarely the real problem. The problem is usually the state of the file underneath it.

A BAS can become stressful when:

Bank feeds have not been reconciled
Transactions have been duplicated
Receipts or tax invoices are missing
GST has been coded incorrectly
Private expenses have been mixed with business expenses
Payroll transactions do not match the ledger
Contractor payments have been allocated to the wrong account
Sales from an integrated platform have not imported correctly
Old unreconciled transactions are still sitting in the file
The Chart of Accounts no longer reflects how the business operates

It’s a bit like trying to bake a cake after discovering the ingredients are scattered across three different kitchens. You might get there eventually, but it will be stressful, messy and full of unnecessary guesswork.

A BAS is only as reliable as the records behind it.

What should you check before lodging your BAS?

Before you press lodge, review the following:

1. Reconcile every relevant bank account

Your bank balance in Xero, MYOB or another accounting platform should agree with the actual bank statement.

Unreconciled transactions can distort your GST figures and make it difficult to tell whether the BAS is accurate.

2. Review GST coding

Check that purchases and sales have been assigned the correct GST treatment.

Common problem areas include:

GST-free purchases
Input-taxed transactions
Overseas transactions
Motor vehicle expenses
Private-use portions
Reimbursements
Asset purchases
Mixed-use expenses

If you are unsure, don’t guess. A small coding mistake repeated across a quarter can create a much larger correction later.

3. Look for duplicates and missing transactions

An integration may import the same transaction twice. It may also fail to import something altogether.

This is where professional accounting software integration support can make a real difference. Your financial platform should be doing the heavy lifting, not quietly creating a second problem in the background.

4. Compare the BAS figures with your reports

Review your GST and sales figures against your:

Profit and Loss report
Balance Sheet
General Ledger
Accounts Receivable
Accounts Payable
Payroll reports

This gives you a broader view of the business and supports more useful financial reporting for small business. You are not simply lodging a form; you are checking whether the numbers tell a believable story.

5. Check unusual movements

If GST collected or GST paid is dramatically different from the previous quarter, investigate before lodging.

There may be a perfectly reasonable explanation, such as a large asset purchase or a seasonal sales increase. But unusual movements deserve a second look rather than a shrug and a hopeful click.

How can you build a BAS routine that removes the panic?

The best BAS process is boring. That is a compliment.

A reliable routine might look like this:

Weekly

Upload receipts and supplier invoices
Review new bank transactions
Resolve missing information
Check that integrations are working

Monthly

Reconcile all bank and credit card accounts
Review GST coding
Run a Profit and Loss report
Follow up unpaid invoices
Check payroll and superannuation records

Four weeks before lodgement

Complete a preliminary BAS review
Identify unusual GST movements
Resolve missing receipts and invoices
Investigate unreconciled transactions
Ask questions while there is still time to get answers

Two weeks before lodgement

Finalise reconciliations
Review reports
Confirm the BAS figures
Arrange payment if required
Lodge early where possible

This routine works because it stops the BAS from becoming a once-a-quarter emergency. Instead, your records are maintained in smaller, manageable steps.

What if your file is already behind?

Sometimes the calendar is not the issue. The file has simply fallen over.

Perhaps your bank feeds have not been reconciled for six months. Maybe the previous system integration duplicated hundreds of transactions. Or your business has grown quickly and the original account structure no longer makes sense.

That does not mean the situation is hopeless. It means you need a plan.

At KB Accounts, our bookkeeping health check reviews your accounts for errors, duplications, omissions and settings that are not working as they should. Where a file needs more intensive attention, our Project Rescue process uses efficient systems to bring it up to date.

We can help with:

BAS preparation and lodgement support
Reconciliations
GST coding reviews
Xero bookkeeping services
Payroll and contractor records
Accounting software troubleshooting
Financial reporting
File clean-ups and project rescue
Ongoing outsourced bookkeeping services

The aim is not simply to get one BAS lodged. It is to build a financial system you can rely on next quarter, too.

Could BAS agent services take the calendar off your plate?

If you are spending evenings untangling transactions, chasing receipts and wondering whether your GST figures are right, it may be time to bring in a strategic partner.

KB Accounts provides BAS agent services in Australia for businesses that want accurate records, clear communication and fewer last-minute surprises. We can manage the BAS rhythm, keep your file moving, troubleshoot the software and give you practical information about what your numbers are saying.

That means less time flying blind and more time running your business.

Your 2026–27 BAS checklist

Before the new financial year gets too busy, save these dates:

28 October 2026: Q1 standard due date
11 November 2026: Q1 online lodgement concession date
25 November 2026: Approximate Q1 agent concession date
1 March 2027: Q2 effective due date for everyone
28 April 2027: Q3 standard due date
12 May 2027: Q3 online lodgement concession date
26 May 2027: Approximate Q3 agent concession date
28 July 2027: Q4 standard due date
11 August 2027: Q4 online lodgement concession date
25 August 2027: Approximate Q4 agent concession date

The big one to remember is Monday, 1 March 2027. Q2 has no extra online or agent concession, so don’t let the usual BAS pattern catch you out.

If your accounts are already feeling messy, you do not have to sort everything alone at midnight.

Contact KB Accounts today to discuss BAS support, a bookkeeping health check or a Project Rescue plan for your business. We’ll help get the numbers in order, keep the calendar moving and give you back some much-needed peace of mind.

Your 2026–27 BAS Calendar: Every Deadline You Need to Know (and the One That Catches Everyone)