What Every Invoice Must Include

The non-negotiable fields

Every invoice you issue should carry the same core fields, in the same place, every time. At minimum: your trading name and ABN; the customer's name; a unique invoice number; the issue date; an explicit due date; an itemised description; the amount payable; and how to pay you.

Consistency matters as much as completeness. When the layout never changes, your customer's accounts team can process you on autopilot, and missing details stand out immediately to you before the invoice ever goes out. A template — whether in your accounting software or a tool such as Merion's invoice templates — turns 'did I include everything?' into a solved problem rather than a nightly worry.

Tax invoice versus plain invoice

If you are registered for GST, most of what you issue will be a tax invoice, and the requirements are stricter. It must display the words 'tax invoice', your ABN, the GST amount (or a statement that the total includes GST), and the GST-inclusive total. For supplies of $1,000 or more, it must also identify the buyer by name or ABN.

If you are not registered for GST, you must not include a GST line at all, and your document is simply an invoice. Charging GST you are not entitled to collect is a compliance problem, not a rounding quirk — so make sure your template matches your actual registration status.

Why the number matters

The invoice number looks trivial, yet it does a lot of quiet work. It gives both sides a single reference for the transaction, lets you track which invoices are open, and is the anchor for matching payments and credit notes. Use a simple sequential scheme and never reuse a number.

When a payment lands short, or a customer claims they 'already paid that one', the number is how you reconcile the truth quickly. Gaps and duplicates, by contrast, make your ledger look careless — and a customer who senses disorganisation is more comfortable letting your invoice slide to the bottom of the pile.

Descriptions and the fields that help

Write descriptions the way the customer thinks about the purchase, not just the way you booked it internally. Reference their purchase order or job name, list quantities and unit prices, and avoid internal codes that mean nothing on their side of the desk. A line item that matches their expectation is a line item they approve without a phone call.

A few optional touches earn their keep: a friendly 'thank you', a clear 'pay by' restatement near the total, and a single obvious payment method. Make the easiest action for the reader the action of paying you, and many will simply take it.