An invoice has one job: to get money moved from one business to another with as little friction as possible. Everything on it either helps that happen or is there because a tax authority needs it.
That is a useful lens, because it sorts the list into two piles. A small number of things are genuinely required. Everything else is convention, and the conventions exist because each one removes a reason for somebody not to pay you. A missing purchase order number is not illegal. It will still park your invoice in a queue for three weeks.
Here is the whole list.
What is actually required?
In Canada, the hard requirements come from sales tax rather than from invoicing law as such. If you are registered for GST or HST, the CRA sets out exactly what your invoice must carry so your client can claim their input tax credit, and what it must carry changes with the size of the invoice.
That is a subject of its own and it is covered in detail in GST and HST on invoices, including the amount thresholds and the registration number that people most often leave off. The short version for this article: your business name, the date, the total, your registration number, a description of the work, your client’s name, and the payment terms. Above 500 dollars you need all of it.
Notice how much of that list you would have included anyway. The tax requirements and the practical requirements overlap almost completely, which is convenient, and it means a well built invoice is usually compliant by accident.
If you are not registered, none of the tax requirements apply to you and you should not be putting a tax line on anything. What follows is then entirely convention. It is still worth following.
What identifies the invoice itself?
An invoice number. Every invoice needs one, it needs to be unique, and it needs to never be reused. This is the handle everyone uses to talk about the document: you, your client, their accounts department, your accountant, and the CRA if it ever comes to that. A payment that arrives with a reference of “INV-0431” can be matched in seconds. A payment referenced “invoice” cannot.
The word “Invoice”. Sounds trivial. It is not. A document headed “Invoice” enters a different workflow at the client’s end than one headed “Quote” or “Statement”, and getting that wrong is a common way to have a document read, approved, and then not paid because nobody realised it was a request for money. The three documents are genuinely different and the distinction matters more than most people expect.
The issue date. The date you raised it, which is what payment terms count from.
The due date. Spelled out as an actual date, not only as terms. More on that below, because it is the single highest leverage line on the page.
How should you number invoices?
Sequentially, with no gaps, in a scheme you decide once and never change.
Sequential matters because gaps invite questions. If your invoices run 0041, 0042, 0044, the reasonable question is what happened to 0043, and “I deleted a draft” is an answer you would rather not be giving during a review.
Beyond that, keep it simple. 2026-0041 gives you the year at a glance and
resets cleanly. INV-0041 is fine. Prefixing per client, as in ACME-014,
looks organised and goes wrong the moment you need to sort every invoice you
have ever raised into one order.
Two things to avoid. Do not start at 1, because INV-0001 tells a new client
exactly how much work you have done, and that is not information you owe them.
Start somewhere unremarkable. And do not encode anything meaningful in the
number beyond sequence and maybe year. An invoice number is an identifier, not
a filing system.
What do payment terms actually mean?
Payment terms say when you expect the money. The conventional forms are short and worth knowing precisely, because they are frequently misread.
Net 30 means the full amount is due 30 days from the invoice date. Not 30 business days. Not 30 days from when they got round to opening it.
Due on receipt means immediately. In practice it means “whenever the next payment run happens”, which is why it is weaker than it sounds.
Net 15, Net 45, Net 60 work the same way with different windows. Net 60 is common from large organisations and is usually presented as non-negotiable. It is often more negotiable than presented.
2/10 Net 30 means a two percent discount if paid within ten days, otherwise the full amount at thirty. This is a real tool and an underused one.
Whatever terms you use, put the actual due date on the invoice as a date. “Net 30” requires the reader to do arithmetic. “Due 24 September 2026” does not. The person processing your invoice is processing a stack of them and will act on the one that tells them when it needs to be done.
What does the client’s accounts department need?
This is the part freelancers skip, and it is where invoices go to sit.
A purchase order or reference number, if they use them. Many organisations cannot pay an invoice that has no PO number against it. Not “will not”. The system refuses. Ask before you invoice whether a PO is needed, and put it on the document if so.
The right contact. The person who hired you is often not the person who pays you. Ask who invoices should go to and whether it should also go to a shared inbox. Sending it only to your day to day contact means your invoice is waiting on somebody who has other things to do.
Complete payment details. However you want to be paid, the details must be on the invoice itself. For a bank transfer that means the institution, transit and account numbers, or an IBAN and SWIFT for an international client. For e-transfer, the exact email address. Making someone email you to ask how to pay adds days.
A clear description of the work. Not “consulting services”. Something the approver recognises as the thing they agreed to buy, ideally in the words they used. An invoice that a manager cannot immediately match to work they authorised gets set aside.
Line items with quantities and rates. Even for a fixed price job, breaking it down shows what the number is made of. It also makes partial disputes possible: a client who queries one line can approve the rest, instead of holding the whole invoice.
Your business details in full. Legal name, and trading name if they differ. Address. Email. If you are incorporated, your business number.
What should you leave off?
Anything you would not want repeated. Your internal costs, your margin, notes about the client. Ledger keeps job costs and private expenses separate from the document the client sees, which is the right shape for this: you can see what a job made without any of it appearing on the invoice.
Passive aggression. “Payment would be appreciated at your earliest convenience” is not a payment term. Say the date.
Terms you will not enforce. An interest charge you never apply teaches clients that your invoice deadlines are decorative. What interest you can actually charge in Canada, and the condition most people miss, is covered in getting clients to pay on time. Read it before you put a percentage on anything.
The short version
Required: your name, the date, the total, a description, the client’s name, payment terms, and if you are registered your GST or HST number.
Everything else on this list is convention, and every convention on it exists because somebody, somewhere, did not pay an invoice that was missing it. A due date written as a date, an invoice number that can be quoted, a PO reference, the right recipient, and payment details that need no follow up question. None of it is difficult. All of it is the difference between thirty days and sixty.
This is general information about invoicing practice, not tax or legal advice. For the tax requirements specifically, the CRA’s own guidance is linked from the GST and HST article above.