A proper invoice is the document that starts the prompt-payment clock, and if yours is defective the clock never starts, so the owner can sit on your money without consequence. To be proper, an invoice must name you and your address, state the date and the exact period or milestone it covers, reference the contract or purchase order, describe the work and quantities, set out the amount and payment terms, and give the payment contact details. This guide is the checklist to run every single time you invoice in a prompt-payment province (Ontario, federal projects, Saskatchewan, Alberta, Manitoba on new contracts, and the Northwest Territories for payment).
Why "proper" is a legal term, not a quality judgment
In the prompt-payment provinces, "proper invoice" is defined in the legislation. Once a proper invoice is delivered to the owner, the owner has 28 days to pay and only 14 days to dispute. A defective invoice is a dead invoice: it triggers no clock, the payer can ignore or reject it without penalty, and you have lost the protection the law was meant to give you. The Ontario Construction Act sets the standard most provinces follow.
A point of confusion for subcontractors: in Ontario, only the prime contractor delivers a proper invoice to the owner. The concept does not apply to a sub's invoice going upward. But you should still invoice to the proper-invoice standard, because your work usually rolls into the prime's monthly invoice, and a clean invoice protects you if the dispute ever reaches an adjudicator.
The checklist: what every proper invoice must contain
Run this list before you send. Miss one and you risk a defective invoice:
- Your name and address. The contractor's legal name and address.
- Invoice date and the period or milestone. Not just a date: state the exact range of work, for example "1 to 31 May 2026", or the contractual milestone the invoice relates to.
- Contract reference. The contract number, purchase-order number or work-order number that identifies the authorization for the work.
- Description and quantity. A clear description of the services or materials supplied, with quantities where it makes sense.
- Amount payable and payment terms. The dollar amount and the terms (the statutory default is 28 days).
- Payment contact. The name, title, mailing address and telephone number of the person or department to send payment to.
- Anything the owner reasonably needs for their accounts-payable system, plus anything else the regulation or your prime contract requires.
Province-specific extras you must not miss
- Alberta: you must state on the invoice that it "is intended to be a proper invoice." This is a statutory requirement, so build the line into your template.
- Ontario (from 1 January 2026): an invoice is deemed proper unless the owner objects in writing within 7 days, setting out how it falls short. This is a defensive win for you: if the owner stays silent past 7 days, they can no longer reject it as defective.
- Federal projects: the proper invoice must also name the federal authority, and the owner's notice-of-non-payment window is 21 days rather than 14.
- Read your prime contract. Owners often add their own proper-invoice requirements, such as a WSIB or WCB clearance certificate, statutory declarations or signed site instructions. If the contract lists them, they are part of "proper" and a missing one makes the invoice defective.
Worked habit: invoice monthly, by default
Unless your contract says otherwise, the statutory default is that you invoice monthly. You cannot be forced to make your invoice conditional on a payment certifier's approval; any such condition is void. So submit on the agreed date every month, with all the elements above, and keep date-stamped proof of delivery. That proof is what starts and protects the clock.
Common mistakes
- Stating a date but not a period. "Invoice dated 31 May" is not enough; you must state the work period or milestone the invoice covers.
- Leaving off the contract reference. No contract or purchase-order number is one of the most common defects.
- Forgetting Alberta's magic line. In Alberta, omitting the statement that it is intended to be a proper invoice can sink it.
- Ignoring the contract's add-ons. A missing clearance certificate or statutory declaration the prime contract demands can make an otherwise complete invoice defective.
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