What is an Invoice?

Invoice definition

An invoice is a commercial document issued by a seller to a buyer that records and requests payment for goods or services. It supports the seller's record of the sale and the amount claimed under the parties' agreement. The underlying contract, delivery and applicable law determine whether and when the amount is enforceable.

In the simplest terms, an invoice answers three questions:

• What was sold? Goods, hours of work, deliverables — itemised with quantities and prices.
• What is owed? Subtotal, GST (if applicable), and the total payable.
• When and how should it be paid? Due date, bank details, payment terms.

Every business that sells goods or services on credit terms — meaning the buyer pays after delivery rather than upfront — uses invoices.

What's on a standard invoice

A clear business invoice commonly has the following 12 fields. In Australia, some are mandatory only for a valid tax invoice; regular invoices do not have one universal statutory field list.

• The header label ("Tax Invoice" or "Invoice")
• Your business name and ABN
• Your contact details (address, email, phone)
• The buyer's name and address
• A unique invoice number
• The issue date
• Line items with descriptions and prices
• The subtotal
• GST (if you are GST-registered)
• The total payable
• Payment terms (e.g., "Net 14")
• Bank details or payment links

See our full invoice checklist for what each field should contain.

What is an itemised invoice?

An itemised invoice breaks the total into separate goods, services, quantities, rates, discounts and tax instead of showing one unexplained lump sum. For example, a contractor might list labour hours, materials, travel and disposal as separate lines.

Itemisation makes an invoice easier to approve, match to a quote or purchase order, and resolve if the customer questions one part of the charge. It also gives both businesses a more useful accounting record.

Include enough detail to identify what was supplied, but avoid confidential notes or internal shorthand the customer cannot understand.

Invoice vs receipt — what's the difference?

People use the words interchangeably, but they are different documents.

• An invoice is a request for payment, issued before payment is made. It creates a debt.
• A receipt is a record of payment, issued after payment is made. It proves the debt has been settled.

On smaller cash sales (a coffee, a parking ticket), the receipt is the only document the buyer sees. On credit sales (most B2B work), the invoice comes first and the receipt — if one is issued at all — confirms payment afterwards.

Invoice vs quote vs proforma — what's the difference?

Three preliminary-vs-final document pairings:

• Quote: an offer to do work at a stated price, used before the buyer commits. In Australia, an accepted quote can become a legally binding contract. See quote vs invoice.
• Proforma invoice: looks like an invoice but is non-binding — used after the quote is accepted and before goods are delivered, often to arrange deposits or letters of credit. See our proforma invoice guide.
• Invoice (tax invoice): the final, binding document issued after goods or services are delivered. Records the sale and triggers GST.

Only an invoice (specifically a tax invoice) creates a debt the seller can enforce and lets the buyer claim a GST credit.

Invoice vs bill — are they the same?

Usually, yes. A seller sends an invoice and the customer records the same document as a bill. Businesses tend to use invoice for itemised work with a document number and payment terms, while bill is common for utilities, restaurants and amounts expected to be paid immediately.

The heading does not decide whether payment is due or whether tax rules have been met — the agreement, due date and required document details do. See the full invoice vs bill comparison.

Invoice vs tax invoice

In Australia, "invoice" and "tax invoice" are not synonyms — they are different documents required in different situations.

• Tax invoice. Issued by a GST-registered business when the sale is $82.50 or more (GST-inclusive). Must include the words "Tax Invoice", the GST amount, and the supplier's ABN. Allows the buyer to claim a GST credit on their BAS.
• Regular invoice. Issued when the seller is not GST-registered, or when the sale is under $82.50. Must not include the words "Tax Invoice" or show GST.

See our tax invoice guide for the full ATO requirements.

How an invoice fits into the sales cycle

The typical Australian small-business sales flow:

1. Quote. Seller proposes the work and price. Buyer accepts (verbally or in writing).
2. (Optional) Proforma invoice. Used when the buyer needs to authorise a deposit or arrange a PO before work begins.
3. Work done / goods delivered.
4. Invoice issued. The seller sends the tax invoice or regular invoice at the agreed billing point — often immediately after completion. See how to send an invoice.
5. Payment. The buyer pays per the stated terms (commonly Net 14 or Net 30).
6. (Optional) Receipt. Issued only if the buyer requests proof of payment.

Both seller and buyer must retain copies of the invoice for 5 years under ATO record-keeping rules.

Frequently asked questions

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