If you have made an error in your gst return, ato has a formal framework for correcting them, and for most small businesses the process is straightforward.

There are two categories of errors:

Credit errors are ones where you reported too much GST payable, or claimed too few input tax credits — you overpaid the ATO. Fixing these gets you a refund or reduces your next payment.

Debit errors are ones where you reported too little GST payable, or claimed too many input tax credits — you underpaid the ATO. Fixing these increases what you owe.

For both types, the ATO allows you to correct errors on a later BAS rather than revising the original BAS, provided you’re within the correction limits based on your business turnover. The specific dollar limits and correction periods change from time to time, so it’s worth confirming the current thresholds directly on the ATO website or with your accountant before deciding how to handle a specific correction.

Corrections on your next BAS. If your error falls within the correction limits, you simply adjust the relevant labels on your next BAS. No formal amendment needed, no penalty, no interest.

Revising the original BAS.

If your GST error exceeds the correction limits, or falls outside the correction period allowed by the ATO, you’ll need to revise the original BAS rather than correct it on a later one.

The correction limits and time periods depend on your current GST turnover.

Time limits for correcting debit errors on a later BAS:

• GST turnover less than $20 million — must be corrected on a BAS lodged within 18 months of the due date of the original BAS in which the error was made
• GST turnover $20 million or more — must be corrected on a BAS lodged within 12 months of the due date of the original BAS in which the error was made.

Value limits for debit errors on a later BAS:

If the net sum of your debit errors exceeds the applicable value limit, you can correct up to the limit on a later BAS and must revise the earlier period for the excess. If the error is outside the 18-month (or 12-month) time limit, the whole correction has to be made through a revised BAS.

Credit errors have no value limit and can be corrected on a later BAS provided you’re within the 4-year period of review from the original lodgement date.

Revised BAS can be lodged through myGov, ATO online services for business, or by your registered tax or BAS agent. General interest charge (GIC) and penalties may apply on debit error revisions, depending on how the error occurred and how quickly it’s disclosed.

If you need help with GST reviews, BAS lodgements, or corrections without unnecessary ATO penalties, get in touch. Outback Accounting works with Australian small businesses to keep it all on track. 

Voluntary disclosure.

• Debit errors above the value limit for your turnover (for example, more than $12,500 in net debit errors for a business with GST turnover under $20 million, or above the higher thresholds shown in the table for larger businesses)
• Debit errors outside the debit error time limit (more than 18 months old for businesses under $20 million turnover, or more than 12 months for businesses at $20 million or above)
• Debit errors resulting from recklessness or intentional disregard of a GST law.

The ATO uses specific terminology for the last category:

In practice, most small business GST errors caught during monthly reconciliation are small enough to correct on the next BAS. The trouble usually starts when errors go unnoticed for multiple quarters and compound.

How to prevent GST errors going forward

Fixing errors is important. Not making them in the first place is better.

Set up your Xero chart of accounts with default tax codes that match how each account should behave. Bank fees default to GST-free. Wages default to BAS Excluded. Motor vehicle expenses default to GST — but with a note to check for personal use. Residential rent, if applicable, defaults to Input Taxed. Getting the defaults right means the automated bank feeds and imported invoices land in the right treatment more often.

Reconcile weekly or monthly, not quarterly. Errors caught within a few weeks of happening are easier to fix and less likely to compound. Errors that sit in the books for three months become harder to unwind.

Review your BAS before lodging. Even five minutes checking the draft against a P&L catches most errors.

Get bookkeeping done by someone who understands GST properly. General bookkeepers vary widely in how carefully they handle tax codes. If your books are being coded by someone who doesn’t have GST training, mistakes will keep happening regardless of how good your software is.

For businesses that regularly deal with complex GST scenarios imports, mixed-use expenses, financial supplies, capital purchases periodic review by a qualified accountant is worth the cost. It’s usually a fraction of what an ATO correction and penalty regime costs.

When to bring in an accountant

Small, occasional GST errors are usually straightforward to fix on your own or with your bookkeeper. Bring in an accountant when:

• You’ve discovered a pattern of errors across multiple BAS periods
• The correction exceeds the ATO’s simple correction limits
• The ATO has contacted you about a discrepancy or is auditing your BAS
• You’re not sure whether a specific transaction should be taxable, GST-free, input taxed, or out of scope
• You’ve moved onto Xero from another system and want the historical GST treatment reviewed
• Your business has started importing, dealing in financial supplies, or added a new revenue stream with unclear GST rules.

Outback Accounting’s accounting team works with Australian small businesses on GST reviews, BAS preparation, and ATO correspondence. If you’ve discovered an error and aren’t sure how to handle it, that’s exactly the kind of thing worth a short conversation to get right.

Our bookkeeping services also focus on getting the GST treatment correct as transactions flow in, rather than fixing them at BAS time.

Frequently asked questions

Can I fix a GST error on my next BAS? Often, yes. For most small businesses (GST turnover under $20 million), debit errors up to a net value of less than $12,500 can be corrected on a later BAS, provided the correction is lodged within 18 months of the due date of the original BAS. Businesses with GST turnover of $20 million or more have a shorter 12-month window but higher value limits — ranging from less than $25,000 (turnover $20m to less than $100m) up to less than $560,000 (turnover $1 billion and over). Credit errors have no value limit and can be corrected on any later BAS lodged within the 4-year period of review from the original BAS lodgement date. 

What happens if I don’t fix a GST error? If the ATO identifies the error during a review or audit, you’ll be required to correct it and may face penalties and interest. Voluntarily fixing errors as soon as you find them either on your next BAS or through a revised BAS usually avoids penalties and shows the ATO that your business is trying to comply. Errors that go uncorrected for years become significantly more costly.

Do I need to revise every incorrect BAS? Not necessarily. Small errors within the ATO’s correction limits can be fixed on your next BAS without formally revising anything. Larger errors, or errors outside the correction period, generally require a revised BAS. A tax agent can advise which approach is appropriate for your specific situation.

How far back can I claim missed GST credits? Under Australian tax law, there’s a four-year limit on claiming input tax credits. If you missed claiming GST on a purchase, you generally have four years from the date of the tax invoice to claim it. After four years, the credit is lost. This is one of the reasons regular reconciliation matters.

What’s the difference between GST-free and input taxed? Both mean no GST is charged, but the treatment of related purchases differs. For GST-free sales (like exports or basic food), you can still claim GST credits on your input costs. For input taxed sales (like residential rent or interest income), you cannot claim input tax credits on related expenses. Misclassifying between these two treatments creates errors on both the sales side and the credit claims side.

Get your GST treatment reviewed

If you suspect there are errors in your current GST coding, or you’ve discovered a problem on a past BAS and aren’t sure how to fix it properly, it’s worth getting professional help before the ATO gets involved.

Outback Accounting works with Australian small businesses on GST reviews, BAS preparation, and corrections that keep you compliant without unnecessary penalties. Get in touch with our team to talk through what’s going on and how to resolve it.