There's a quiet deadline ticking away inside your BAS history right now — and if you miss it, the ATO won't give you a second chance.

Every GST credit you're entitled to has a hard expiry date: 4 years from the due date of the BAS in which you could have first claimed it. After that, the credit is gone. Not deferred. Not renegotiable. Gone. The ATO has no discretion to extend it, no process to revive it, and no sympathy for businesses that discover the mistake too late.

Most business owners don't know this rule exists until they're staring at a tax invoice from 2022 and wondering why their accountant can't just "add it to this quarter's BAS." The answer is Division 93 of the GST Act — and thanks to the ATO's Miscellaneous Taxation Ruling MT 2024/1, the rules are now stricter and clearer than ever.

Why This Matters Right Now

If you lodge your BAS quarterly — like most small businesses — credits from the January–March 2022 quarter are approaching their expiry date. The BAS due date for that period was 28 April 2022, which means the 4-year credit window closes on 28 April 2026. That's one month away.

And here's the part that catches people out: the ATO doesn't just need to receive your amendment request within 4 years. They need to process it and include it in your assessment within that window. If you lodge an amendment on 25 April and the ATO processes it on 30 April, those credits are dead.

This isn't hypothetical. The ATO confirmed this interpretation in MT 2024/1, building on the Full Federal Court's decision in Linfox Australia Pty Ltd v Commissioner of Taxation [2019] FCAFC 131. The ruling makes clear that amendment requests, voluntary disclosures, and even private ruling applications don't preserve your entitlements. Only one thing does — and most businesses don't know about it.

How the 4-Year Rule Actually Works

The rule lives in Division 93 of the A New Tax System (Goods and Services Tax) Act 1999. Here's how the clock ticks.

When the Clock Starts

The 4-year period begins on the due date of the BAS for the tax period in which you could have first claimed the credit. Not the date you actually lodged. Not the date you paid the invoice. The original BAS due date.

This means:

Reporting Period	BAS Due Date	Credit Expires
Jan–Mar 2022 (quarterly)	28 April 2022	28 April 2026
Apr–Jun 2022 (quarterly)	28 July 2022	28 July 2026
July 2022 (monthly)	21 August 2022	21 August 2026
Oct–Dec 2022 (quarterly)	28 February 2023	28 February 2027

Cash vs. Accruals: The Starting Point Differs

How you account for GST changes when the clock starts ticking:

Accruals basis: The credit arises in the tax period when the invoice is issued or payment is made — whichever happens first. This means the clock can start before you've actually paid for the purchase.

Cash basis: The credit arises in the tax period when you make the payment. If you pay in instalments, the 4-year limit applies separately to each payment. A deposit in March 2022 and a final payment in June 2022 have different expiry dates.

The Tax Invoice Wrinkle

Here's a detail that trips up a lot of businesses: the 4-year clock starts based on when you could have first claimed the credit, "setting aside any requirement to hold a tax invoice." In other words, not having a tax invoice doesn't stop the clock. If you were entitled to the credit but didn't claim it because you were chasing a missing invoice, the 4-year period was already running.

You can claim a GST credit without a tax invoice if the total is $82.50 or less (GST inclusive). For anything above that, you need the invoice — but the clock doesn't wait for you to get it.

What MT 2024/1 Changed

The ATO released MT 2024/1 on 4 December 2024, and it substantially tightened the rules around what counts as "taking a credit into account" within the 4-year period.

What Preserves Your Credits

Only one thing reliably protects your entitlement: a valid objection lodged within the 4-year period. If you object to an assessment and the objection (or subsequent appeal) confirms your entitlement, the credit survives even if the decision comes after the 4-year window closes.

What Doesn't Preserve Your Credits

This is where most businesses — and some advisers — get caught out:

Amendment requests — lodging a request to amend your BAS does not stop the clock. If the ATO processes it after the 4-year deadline, the credits are lost.
Private ruling applications — asking the ATO for a ruling on whether you're entitled to a credit does not extend the deadline.
Voluntary disclosures — coming forward to correct an error doesn't preserve the credit either.

As Kelly Partners put it, the only protective mechanism is "lodging a formal objection within the four-year window."

The Linfox Precedent

MT 2024/1 is built on the Full Federal Court's decision in Linfox Australia v Commissioner of Taxation [2019] FCAFC 131. The court established that a credit is "taken into account" in an assessment only to the extent that the amount representing the credit forms part of the calculation that produced the assessed amount.

In practical terms: if you didn't include the credit in your BAS and the ATO didn't include it in their assessment of your net amount, the credit was never "taken into account" — and the 4-year clock kept ticking regardless.

The Asymmetry That Should Worry You

Here's the part of Division 93 that keeps tax advisers up at night: there is no equivalent 4-year expiry on your GST liabilities.

If you failed to lodge a BAS for a period, or you understated your GST on sales, the ATO can still assess you for that GST — potentially going back well beyond 4 years in cases of fraud or evasion. But your input tax credits from that same period? Gone after 4 years.

This creates a brutal outcome for businesses with unfiled historical BAS returns. When a new accountant uncovers years of unlodged BAS statements, they'll find that GST on sales is still owing — with penalties and interest — but the GST credits that would have offset those liabilities have expired. The business gets hit with the full bill, reduced by nothing.

As Kelly Partners noted, this is a "significant quirk" where "a business may lose its right to claim ITCs through inaction but remain liable for GST owing on sales."

Where Businesses Commonly Lose Credits

Understanding the rule is one thing. Knowing where credits actually slip through the cracks is another. Here are the most common scenarios.

1. Delayed BAS Lodgement

You're busy running a business. The BAS gets pushed back a quarter, then another. By the time you catch up, credits from 3–4 years ago are either expired or dangerously close.

2. Poor Invoice Management

A supplier sends an invoice without proper GST details. You set it aside to follow up. Two years later, you find it in a drawer. The credit was claimable — the clock started when the invoice was first issued — but now half the 4-year window is gone.

3. Changing Accountants

The transition between accountants is a black hole for GST credits. The old accountant didn't claim something. The new accountant doesn't know it was missed. By the time someone notices, the window has closed.

4. Mixed-Use Assets

You buy a vehicle for 70% business use. Your bookkeeper isn't sure how to apportion the GST credit, so they leave it out of the BAS "to be safe." That conservative approach just cost you the entire credit if nobody revisits it within 4 years.

5. Capital Purchases Coded Incorrectly

A $50,000 piece of equipment gets coded as a non-GST purchase in the accounting software. The GST credit — $4,545 — sits unclaimed. Nobody reviews the coding. Four years later, that's $4,545 you'll never see again.

6. Cash Basis Instalment Payments

You're on a cash basis and pay a large invoice in three instalments across different quarters. Each instalment triggers a separate GST credit with its own 4-year deadline. Miss one, and you lose the credit for that portion — even if you claimed the others.

Common Mistakes to Avoid

Mistake #1: "I'll just add the missed credit to this quarter's BAS"

You can claim a GST credit in a later BAS — but only if it's still within the 4-year window. You can't claim a credit from Q1 2021 on your March 2026 BAS. The window closed in April 2025.

Mistake #2: "I've lodged the amendment, so I'm covered"

Lodging an amendment request is not the same as having it processed. The credit must be included in an assessment before the deadline. If the ATO takes weeks to process your amendment and the deadline passes in between, the credit is lost. MKT Taxation Advisors confirmed that "other processes such as requesting an amendment to an assessment or applying for a private ruling do not provide the protections that exist for the objection process."

Mistake #3: "The 4-year period starts from when I paid the invoice"

Only if you're on a cash basis. On accruals, it starts from when the invoice was issued or payment was made — whichever is earlier. The due date of the BAS for that period is what matters, not the transaction date.

Mistake #4: "I didn't have the tax invoice, so the clock hasn't started"

The ATO calculates the 4-year period "setting aside any requirement to hold a tax invoice." The clock runs regardless of whether you have the documentation. Not having an invoice is a separate problem — it doesn't pause your deadline.

What You Should Do Now

1. Run a GST credit reconciliation for 2021 and 2022

Why: Credits from early 2022 are expiring in the next few months. If you haven't reviewed your BAS lodgements for that period, unclaimed credits could be vanishing right now. When: This week. Seriously. The January–March 2022 quarter expires on 28 April 2026.

2. Check for unlodged or amended BAS periods

Why: If you have any unlodged BAS returns from 2022 or earlier, the GST credits for those periods may already be gone — but the liabilities aren't. You need to understand the exposure before the gap widens further. When: Immediately, especially if you've changed accountants in the last few years.

3. Lodge a formal objection if credits are disputed

Why: An objection is the only process that reliably preserves your credit entitlement beyond the 4-year window. Amendment requests and private rulings do not. If you believe you're entitled to credits and the deadline is approaching, an objection is your safeguard. When: Before the 4-year deadline for the relevant period. Once it passes, objections can't revive the credit either.

4. Review your accounting software coding

Why: Miscoded purchases — especially capital items, mixed-use assets, and large one-off expenses — are the most common source of missed GST credits. A quick review of your GST account codes can surface thousands of dollars in unclaimed credits. When: As part of your next BAS preparation. Build this into your quarterly routine.

5. Set up a quarterly GST credit review process

Why: The businesses that lose credits are the ones that never look back. A 15-minute reconciliation each quarter — comparing GST paid on purchases against credits claimed on BAS — catches errors while there's still time to fix them. When: Starting this quarter. Use accounting software reports to flag purchases where GST was paid but no credit was claimed.

The Bottom Line

The GST 4-year credit window is one of the harshest deadlines in Australian tax law — not because it's short, but because it's absolute. No extensions. No discretion. No second chances. And thanks to MT 2024/1, the ATO has made clear that amendment requests and private rulings won't save you if the clock runs out.

The good news? Four years is a generous window if you use it. Regular BAS reviews, clean bookkeeping, and a quarterly reconciliation habit will catch missed credits well before they expire. The businesses that get burned are the ones that assume someone else is watching the clock.

If you haven't reviewed your 2022 BAS periods, do it now. April deadlines are approaching, and every missed credit is money you've already spent that you'll never get back.

Sources & Further Reading

Disclaimer: This article provides general information only and does not constitute tax, legal, or financial advice. The application of tax law depends on individual circumstances. Always consult a qualified tax professional before making decisions about your GST credit claims.

The GST 4-Year Credit Window: Claim It or Lose It