You've already sent the invoice, the client has it on file, and then you realise you undercharged them. Maybe extra goods were added to the order last minute, or a Goods and Services Tax (GST) figure wasn't calculated correctly. Now you need to correct the record without voiding everything and starting over.
That's exactly what a debit note is for.
Whether you run a café in Fitzroy, a retail shop in Newtown, or a trade services business across the suburbs, understanding how debit notes work, and when Australian tax law requires something slightly different, can save you from costly billing errors and messy BAS reconciliations.
What is a debit note?
A debit note (also called a debit memo) is a formal document issued by a seller to notify a buyer that their account has been debited. This means they owe additional money beyond what the original invoice stated.
It typically comes into play when:
- The original invoice was too low due to a pricing or data entry error
- Additional goods or services were delivered after the invoice was sent
- A discount was applied incorrectly and needs to be reversed
- GST was omitted or calculated at the wrong rate
Think of it as a correction document that increases the amount owed without creating a new transaction from scratch.
What is a debit note in accounting?
In accounting, a debit note is used to record and formalise an upward adjustment to an existing invoice. It creates a clear paper trail that both parties can reference during reconciliation, audits, or disputes.
From the buyer's side, receiving a debit note means their accounts payable balance increases as they now owe more than the original invoice stated. From the seller's side, issuing one means their accounts receivable balance increases as they now expect to collect more.
For Australian businesses, it's worth knowing that accounting software like Xero and MYOB handles debit notes and adjustment notes within the same workflow, but the terminology in your tax reporting needs to align with what the ATO expects.
Debit notes and the ATO: What is an adjustment note?
If your business is registered for GST, the term "debit note" has a specific counterpart in Australian tax law. When a billing adjustment affects a taxable supply, for example, you invoiced $1,000 + GST but should have charged $1,200 + GST, the ATO requires an adjustment note, not simply an amended invoice.
An adjustment note must include:
- The words "adjustment note" (or similar wording that clearly identifies it as such)
- Your Australian Business Number (ABN)
- The date of the adjustment
- A brief description of why the adjustment is being made
- The amount of the GST adjustment
Both the supplier and the recipient may need to update their GST credits or obligations in the relevant BAS period. Operators should verify specific requirements directly with the ATO or a registered tax agent, as the rules can vary depending on the size of the adjustment and your reporting cycle.
What is the difference between a debit note and an invoice?
This is one of the most common questions Australian business owners ask. Here's how they differ:
|
Invoice |
Debit note |
| Purpose |
Request initial payment for goods or services |
Adjust an existing invoice upward |
| When issued |
At point of sale or service delivery |
After the original invoice, when more is owed |
| Accounting impact |
Creates accounts receivable |
Increases existing accounts receivable |
| GST implication |
Original tax invoice |
May require an adjustment note for GST purposes |
| Initated by |
Seller |
Seller (or buyer, as a formal correction request) |
The key difference: an invoice is the original billing document. A debit note is an amendment that says, "the amount on that invoice wasn't enough."
What is a debit note and a credit note, and how are they different?
Debit notes and credit notes are often mentioned together because they are two sides of the same coin. Both are post-invoice adjustments, but they move in opposite directions.
What is a debit note?
A debit note increases the amount owed. It's issued when the original invoice was too low, because of a pricing error, additional goods delivered, or a charge that was left off.
Example: You invoice a client $800 for a catering job, then realise the setup fee wasn't included. You issue a debit note for $200, bringing the total to $1,000.
What is a credit note?
A credit note decreases the amount owed. It's issued when the buyer returns goods, an overcharge occurred, or a discount is applied after invoicing.
Example: A customer returns a faulty product from an online order. You issue a credit note for the returned item value, reducing the amount they owe (or triggering a refund).
Side-by-side comparison
|
Debit Note |
Credit Note |
| Effect on amount owed |
Increases it |
Decreases it |
| Common reason |
Undercharge, extra goods, missed fees |
Overcharge, returns, post-invoice discounts |
| Buyer's accounts payable |
Goes up |
Goes down |
| Seller's accounts receivable |
Goes up |
Goes down |
| ATO equivalent (GST) |
Increasing adjustment note |
Decreasing adjustment note |
When do you need both?
Some transactions require a credit note and a debit note in sequence. For example, if an invoice is cancelled and reissued at a different price, you may issue a credit note to zero out the original, then a debit note (or new invoice) to reflect the corrected amount.
In practice, most accounting software handles both document types within the same workflow. The important thing is that each adjustment is linked to the original invoice reference and filed correctly before your BAS is lodged.
When should you issue a debit note?
Not every billing adjustment needs a debit note, but there are clear situations where it's the right tool.
Common scenarios for Australian SMEs:
- A trade services business invoices for labour but forgets to include materials
- A wholesaler delivers additional stock after the original order was invoiced and paid
- A professional services firm realises their quoted fee excluded a disbursement
- An online retailer needs to recover a shipping shortfall not captured in the original order total
When not to use one: if the original transaction hasn't been invoiced yet, just update the invoice. Debit notes are correction tools, not replacements for accurate invoicing in the first place.
How debit notes affect cash flow and reconciliation
For most Australian SMEs, the bigger challenge isn't understanding what a debit note is, it's making sure billing adjustments don't create problems at BAS time.
Unrecorded debit notes can cause:
- Understated revenue: Your books show less than you actually earned
- GST errors — your BAS may underreport GST collected if adjustment notes aren't captured in the right period
- Reconciliation gaps: Bank deposits don't match recorded sales
- Client disputes: Without documentation, conversations about additional charges become difficult
Many debit notes stem from the same root cause: an original transaction record that was incomplete or rushed. That's often a signal to tighten the billing process — starting at the point where the sale is first recorded.
How Australian SMEs can reduce billing errors
Get the transaction record right at the point of sale
For retail, hospitality, and service businesses, most billing errors trace back to what was captured when the sale happened. If your payment system records transactions with clear itemised data, you have a reliable reference point when a query arises.
KPay Terminal Pro records each in-store card transaction with itemised detail and daily settlement reports, giving you a clean audit trail to work from. When a client questions a charge or you need to issue a debit note, you can reference the original transaction record immediately.
Capture billing adjustments before sending invoices for remote payments
Debit notes often arise because the invoice sent to a client didn't reflect what was actually agreed or delivered. For businesses billing clients remotely, such as trades, professional services, and B2B suppliers, sending a Payment Link alongside the invoice creates a direct digital record of the transaction amount at the time of payment.
If a discrepancy is caught before the client pays, you can correct the amount in the payment link before it's settled, reducing the need for a follow-up debit note.
Reconcile across your online and in-store channels
Australian businesses increasingly take payments across multiple channels, such as in-store card terminals, online checkout, and direct payment requests. When each channel operates separately, reconciliation becomes harder and billing gaps are easier to miss.
KPay's Payment Gateway supports online transaction processing with clear settlement reporting, making it easier to cross-reference online sales against your invoicing records. Regular reconciliation — ideally weekly rather than monthly — catches discrepancies before they roll into your BAS period.
Work with an accountant on GST adjustment notes
If you're issuing or receiving debit notes that affect GST-applicable supplies, involve your accountant or BAS agent before lodging. The rules around adjustment note timing, ABN requirements, and which BAS period the adjustment falls into are worth getting right.
Australia has a strong base of small business accountants and bookkeepers familiar with Xero and MYOB workflows. If billing adjustments are becoming a regular occurrence, a short review of your invoicing process with a professional can save significant time at tax time.
Accurate billing starts before the invoice is sent
A debit note is a useful tool, but the goal is to need it as rarely as possible. For Australian businesses, that means capturing transaction data accurately at the point of sale, reconciling regularly across payment channels, and understanding when the ATO's adjustment note requirements apply.
