Australia GST Adjustment Notes: Requirements and Practical Guide

An adjustment note is Australia's GST-specific document that records a change to the GST amount on a previously issued tax invoice. Defined under the A New Tax System (Goods and Services Tax) Act 1999, it serves a narrow but critical function: when the price, scope, or GST treatment of a taxable supply changes after the original tax invoice has been issued, an adjustment note formally documents that change for both parties and for the Australian Taxation Office (ATO).

If you've worked with GST or VAT systems outside Australia, you're probably used to issuing a credit note when something changes. Australia does things differently. An adjustment note is not a credit note under another name. A credit note typically cancels or replaces the original invoice, effectively rewriting the transaction. An adjustment note, by contrast, documents a specific adjustment event — a price reduction, a returned item, an overstated GST amount — without voiding the original tax invoice. The original invoice stands; the adjustment note records what changed and by how much.

This distinction matters practically, not just terminologically. An adjustment note is required whenever a GST adjustment exceeds $75. Below that threshold, the adjustment can still be made on the Business Activity Statement (BAS), but neither party is obligated to issue or hold a formal adjustment note. Above it, the recipient needs one to claim a corresponding adjustment on their own BAS. Missing or incorrect adjustment notes create mismatches between supplier and recipient GST reporting, which is exactly the kind of error the ATO's compliance systems are designed to detect.

The scale of GST compliance errors in Australia underscores why these details matter. According to the ATO's latest GST gap analysis, the net GST gap reached $8.7 billion for 2023–24, representing 9.4% of theoretical GST revenue. Nearly one in ten GST dollars goes uncollected due to errors, fraud, and non-compliance. Adjustment notes sit squarely within this problem: they are one of the mechanisms that keep GST reporting accurate across the supply chain.

The ATO's own guidance on adjustment notes is fragmented across multiple pages, cross-referenced with rulings, and written in dense legislative language. This guide covers when an adjustment note is required, what it must contain, how increasing and decreasing adjustments work, and how to report them on the BAS.

Adjustment Notes vs Credit Notes: The Australian Distinction

In most GST, VAT, and sales tax jurisdictions, a single document handles invoice corrections. The UK, EU, New Zealand, and North America all use the credit note or credit memo for everything from partial refunds to full cancellations. Australia's GST system introduced a separate correction mechanism — the adjustment note — that sits alongside the credit note but serves a distinct purpose. Understanding the boundary between these two documents is essential for anyone processing GST transactions.

A credit note in Australian practice cancels or reverses the original tax invoice. It effectively unwinds the transaction, often paired with a new, corrected tax invoice if the commercial relationship continues. The original invoice is superseded. For a deeper look at how credit notes and invoices interact, the core mechanics are the same across most tax systems.

An adjustment note does something fundamentally different. It records a specific GST adjustment event without cancelling the original tax invoice. The original invoice remains valid and on the record. The adjustment note documents what changed, why it changed, and the precise GST impact of that change. It modifies the GST position rather than replacing the underlying transaction.

This distinction matters more than it might appear at first glance:

Dimension	Credit Note	Adjustment Note
Purpose	Cancel or reverse an original tax invoice	Record a GST adjustment event
Effect on original invoice	Supersedes or invalidates it	Original invoice remains valid
When used	Transaction is cancelled, voided, or reissued	Price change, partial return, change of use, or other adjustment event after the original supply
GST treatment	Reverses the GST from the original transaction	Adjusts GST by the specific amount of the change
Relationship to original	Replaces it (often with a new corrected invoice)	References the original; both documents coexist

The ATO requires an adjustment note — not a generic credit note — to support a claim for a decreasing adjustment on your BAS. If you issue a standard credit note where an adjustment note was needed, you risk delays in claiming your GST credit or, worse, having the claim rejected on review.

One persistent source of confusion is accounting software. Platforms like Xero, MYOB, and QuickBooks default to labelling all correction documents as "credit notes," regardless of whether the correction constitutes a full reversal or a GST adjustment. If your software generates a document called "credit note" for what is actually an adjustment event, verify that it includes the words "adjustment note," a reference to the original tax invoice number and date, and the GST adjustment amount stated separately. Some platforms generate compliant documents automatically when you process a credit against an existing invoice; others require manual configuration to include all ATO-required fields. The label on the document matters less than its content — but only if the content is actually compliant.

Australia is not the only jurisdiction with this kind of terminological split. Germany maintains its own parallel distinction between the Gutschrift and Stornorechnung, which creates similar confusion for practitioners navigating German credit notes. In both countries, the core challenge is the same: correction documents that look similar on the surface but carry different legal and tax consequences.

When an Adjustment Note Is Required

Not every GST adjustment triggers the obligation to issue an adjustment note. Three conditions must all be satisfied before the requirement kicks in:

A tax invoice was previously issued for the original transaction.
An adjustment event has occurred that changes the GST amount on that transaction.
The GST adjustment exceeds $75.

If any one of these conditions is not met, no adjustment note is required.

The $75 GST Threshold

The $75 figure refers specifically to the change in the GST component, not the change in the total price. A price reduction of $800 on a GST-inclusive supply changes the GST by $72.73. Because that falls at or below $75, no adjustment note is needed. A price reduction of $830 changes the GST by $75.45, which crosses the threshold and does require one.

This distinction matters because practitioners sometimes confuse the total value of the adjustment with the GST impact. Where the GST adjustment is $75 or less, you still need to account for it and report the adjustment on your BAS. The recording and reporting obligation exists regardless. What falls away is only the requirement to issue the formal adjustment note document.

The 28-Day Deadline

Once a supplier becomes aware that an adjustment event has occurred, they have 28 days to issue the adjustment note. The same 28-day window applies when a recipient requests an adjustment note from the supplier. The clock starts from whichever event occurs first: the supplier's awareness or the recipient's request.

Missing this deadline does not eliminate the underlying GST adjustment. The adjustment still needs to be reported in the correct BAS period. But failing to issue the note on time can create compliance exposure and leaves the recipient without the documentation they need to claim their own corresponding adjustment.

Common Events That Trigger the Requirement

Situations where an adjustment note will typically be required (assuming a tax invoice was already issued and the GST change exceeds $75):

A negotiated price reduction after the original invoice was paid
Goods returned by the purchaser for a refund or credit
Services cancelled partway through a contract period
Volume or loyalty discounts applied retrospectively once a purchasing threshold is reached
GST charged incorrectly on the original invoice, discovered after the fact

When the Requirement Does Not Apply

Certain categories of adjustment follow their own legislative rules and sit outside the standard adjustment note framework. Bad debt adjustments under Division 21 are the most common example. When a supplier writes off a debt as bad, the GST adjustment is handled through the BAS without issuing an adjustment note to the debtor. The supplier claims the adjustment based on their own records and the debt write-off criteria rather than through the note exchange process that applies to other adjustment events.

Increasing and Decreasing GST Adjustments

The ATO classifies every GST adjustment as either decreasing or increasing, based on the direction of the change to net GST payable. Getting the classification right determines who owes what and which party needs to adjust their input tax credit claims.

A decreasing adjustment reduces net GST payable. It arises when GST has been overpaid relative to what the transaction actually requires. Common triggers include price reductions after the original tax invoice, returned goods, or cancelled services. The supplier receives a GST credit (reducing what they owe the ATO), while the recipient must reduce their previously claimed input tax credit by a corresponding amount.

An increasing adjustment does the opposite: it raises net GST payable. This occurs when GST was underpaid on the original transaction. Typical causes include a price increase negotiated after invoicing, a supply initially treated as GST-free that is later reclassified as taxable, or a previously estimated consideration that turns out to be higher. The supplier owes additional GST to the ATO, and the recipient can claim an additional input tax credit.

	Decreasing Adjustment	Increasing Adjustment
Effect on net GST	Reduces GST payable	Increases GST payable
Supplier impact	Receives a GST credit	Owes additional GST
Recipient impact	Must reduce input tax credit	Can claim additional input tax credit
Who typically issues	Supplier	Supplier
Example scenario	Supplier grants a $1,100 discount on a completed order; GST component drops by $100	A supply originally invoiced as GST-free is reclassified as taxable, adding $500 in GST

The supplier is generally responsible for issuing the adjustment note in both cases. If the supplier has not issued one within 28 days, the recipient can formally request it.

The practical stakes differ by adjustment type. For a decreasing adjustment, the recipient needs the adjustment note to substantiate the reduction in their input tax credit claim. Without it, they risk over-claiming credits and facing penalties on review. For an increasing adjustment, the recipient needs the adjustment note to support claiming the additional input tax credit. Missing or delayed notes in either direction create a mismatch between what the parties report and what the ATO expects to see.

What an Adjustment Note Must Contain

A valid adjustment note under Australian GST law must include specific information so the ATO can verify the adjustment and both parties can correctly report it. Missing even one required element can invalidate the document, leaving the recipient unable to claim a GST credit adjustment.

Every adjustment note must contain the following:

The words "adjustment note" — the document must be clearly identifiable by this title, not labelled as a credit note, debit note, or any other term.
The supplier's identity and Australian Business Number (ABN) — the same details that appeared on the original tax invoice. If the original supply involved a supplier who did not quote an ABN, separate no-ABN withholding obligations apply to that payment, which must be addressed independently of the adjustment note process.
The date of issue — when the adjustment note was created, not the date of the original transaction.
A reference to the original tax invoice — both the invoice number and its date, so the adjustment can be traced back to the specific transaction being corrected.
The nature of the adjustment — a plain description of what changed and why. For example, "return of 50 defective units from purchase order 4821" or "price reduction per renegotiated contract terms effective 1 March 2026."
The amount of the GST adjustment — the dollar figure by which the GST has increased or decreased, stated separately from the adjustment to the sale price itself.

For larger adjustments, there is an additional requirement. When the GST adjustment exceeds $1,000, the adjustment note must also include the recipient's identity or ABN. This threshold mirrors the rule that applies to tax invoices above $1,000 and exists so the ATO can cross-reference both parties' BAS reporting on significant corrections.

Many of these fields will look familiar to anyone who already understands Australian tax invoice requirements. The adjustment note largely mirrors the tax invoice structure, with two key additions: the reference back to the original invoice and the explanation of what changed. Practitioners who have their tax invoice processes right will find adjustment notes straightforward to produce.

There is no mandated format or official template. The adjustment note can be a standalone document, a section within a broader communication, or a system-generated record, provided it clearly contains every required field and is identifiable as an adjustment note. Most accounting software packages generate compliant adjustment notes automatically when configured with the correct business details and linked to the original invoice.

Common Scenarios That Trigger Adjustment Notes

The rules around adjustment notes are clearer when you see them applied to transactions you actually deal with. Here are four situations that come up repeatedly in practice, along with the correct GST treatment for each.

Price Reduction After Invoice

A supplier issues a tax invoice for $1,100 (including $100 GST) for consulting services. The client negotiates a $220 discount after the invoice has been issued and reported on the supplier's BAS.

The GST component of the $220 reduction is $20, making this a decreasing adjustment. The supplier claims less GST, and the recipient reduces their input tax credit by $20.

Because the GST adjustment amount is $20, which falls below the $75 threshold, no adjustment note is required. Both parties must still record the adjustment in their accounts and report it on their next BAS. The adjustment belongs in the BAS period when the price reduction was agreed, not the period of the original invoice.

Returned Goods

A retailer returns $880 worth of stock (including $80 GST) from a larger wholesale order. The goods were defective, and the supplier agrees to a full refund for the returned portion.

The GST adjustment is $80, a decreasing adjustment that exceeds the $75 threshold. The supplier must issue an adjustment note within 28 days of the return being agreed. The supplier reduces GST payable by $80, and the retailer reduces input tax credits by the same amount.

Report this adjustment on the BAS for the period in which the return occurred. If the original purchase was in the March quarter but the return happened in June, the adjustment appears on the June BAS.

Incorrectly Charged GST

A supplier charges 10% GST on a supply that should have been GST-free. This happens regularly with basic food items sold to commercial buyers, exported goods where the zero-rating was missed, or supplies to entities that provided an exemption declaration.

The entire GST amount is a decreasing adjustment. The supplier needs to issue an adjustment note so both parties can correct their GST positions. The supplier reduces GST payable by the incorrectly charged amount, and the recipient reverses any input tax credit they claimed on that GST.

When correcting GST errors in Australia, timing matters. The adjustment is reported on the BAS for the period when the error is identified, not backdated to the original transaction. If the error spans multiple invoices, each one that exceeds the $75 GST threshold requires its own adjustment note.

Price Increase After Invoice

A supplier discovers a pricing error on an invoice already issued. The contracted rate was $5,500 plus GST, but the invoice was raised for $4,400 plus GST. The underbilled amount is $1,100, with an additional $110 in GST.

This is an increasing adjustment. The supplier issues an adjustment note for the additional $1,100 plus $110 GST, bringing the total to the correct amount. The supplier reports additional GST payable, and the recipient can claim the extra $110 as an input tax credit.

The adjustment note should reference the original tax invoice number and clearly state the additional amount. Report the increasing adjustment on the BAS for the period when the pricing error was identified and the adjustment note issued.

Recording Adjustment Notes on Your BAS

GST adjustments are reported on the Business Activity Statement for the tax period in which the adjustment event occurred. This is the period when the price change, cancellation, or other triggering event actually took place, not the period of the original transaction and not necessarily the period when the adjustment note was issued or received.

Getting the correct BAS labels right matters. Where adjustments appear depends on whether you are the supplier or the recipient, and whether the adjustment increases or decreases the GST amount.

For suppliers:

Decreasing adjustments (where you overcharged GST and now owe less) reduce the amount reported at label 1A (Total sales subject to GST). If you report on a non-cash basis, the reduction may instead be reflected at label 1B.
Increasing adjustments (where you undercharged GST and now owe more) increase the amount at label 1A.

For recipients:

Adjustments that affect input tax credit claims are reported at label G10 for capital acquisitions or label G11 for non-capital acquisitions. A decreasing adjustment on the supplier's side typically means the recipient must also reduce their previously claimed input tax credits at the relevant label, and vice versa.

The Four-Year Time Limit

GST credits arising from prior-period adjustments can only be claimed within four years of the original tax period to which the adjustment relates. If an adjustment event occurs today but relates to a transaction from several years ago, check whether the four-year window is still open before including the adjustment on your current BAS. Claims lodged outside this window will be refused, and amending a BAS beyond the four-year limit requires specific ATO authority.

A Common Reporting Mistake

One of the most frequent BAS errors with adjustment notes is reporting the adjustment in the period the note was received rather than the period the adjustment event occurred. These dates often differ. A supplier might issue an adjustment note in July for a price reduction agreed in June. The adjustment belongs on the June-quarter BAS, not the September quarter. Reporting in the wrong period can create mismatches that trigger ATO review notices or require later BAS amendments.

When recording adjustment notes, retain them alongside the original tax invoices they relate to. The ATO expects businesses to substantiate their GST position with a complete documentation chain linking the original supply, the adjustment event, and the adjustment note. Having these records grouped and accessible is essential for audit readiness and for resolving any ATO queries without delay.