Construction services and materials are taxable supplies, so the tax itself is straightforward: the federal rate is 5%, with an additional provincial component in the participating provinces. What trips contractors up is timing — the Excise Tax Act contains a rule written specifically for construction contracts expected to run more than three months, and a separate treatment for holdback.
Key takeaways
Two contractors bill the same job the same way and end up in different places with the Canada Revenue Agency — one remitted tax on money that had not arrived, the other failed to remit on money that had. Both errors come from treating a construction contract like an ordinary invoice.
Section 165(1) of the Excise Tax Act imposes tax on every recipient of a taxable supply made in Canada calculated at the rate of 5% on the value of the consideration for the supply. Section 165(2) adds that a recipient of a taxable supply made in a participating province pays, in addition, tax calculated at the tax rate for that province. The Act deliberately does not print the provincial numbers in that section — they are set elsewhere and have changed before. In Ontario the combined rate is 13%, as our sister firm sets out in its explanation of HST on construction services and materials. If you work across provincial lines, confirm the rate for each province rather than assuming your home rate travels with you.
Section 168(1) sets the general rule: tax is payable by the recipient on the earlier of the day the consideration for the supply is paid and the day the consideration becomes due. Section 168(2) applies that separately where consideration is paid or becomes due on more than one day — which is precisely what a progress billing is — so tax is payable on each such day, calculated on the value of the part paid or becoming due on that day.
Then comes the provision written for this industry. Section 168(3) says that where all or part of the consideration has not been paid or become due on or before the last day of the calendar month immediately following the first calendar month in which a specified event occurs, tax on that consideration is payable on that day. For construction, that event is set out in paragraph (c): a supply under a written agreement for the construction, renovation or alteration of, or repair to, real property, where it may reasonably be expected that the work will require more than three months to complete, with the trigger being substantial completion.
Read that slowly, because the shape matters. It is a backstop, not a deferral. It does not delay tax on amounts already paid or already due — those are caught by 168(1) and (2) as usual. What it does is ensure that consideration still floating at substantial completion cannot sit outside the system indefinitely: it becomes payable by the end of the month following the month of substantial completion. On a long job with a slow final billing, that date can arrive before the invoice does.
Three dates to keep on a long contract
Each progress billing. Tax on that part is payable on the earlier of payment and the day it becomes due.
Substantial completion. Record it. Section 168(3) counts from the calendar month in which it happens, not from the final invoice.
Holdback release. Treated on its own timing — see below.
Because holdback is money the contractor is required to leave unpaid, taxing it on the same day as the rest of the progress billing would mean remitting tax out of pocket on funds nobody has. Our sister firm explains that construction contracts get special timing treatment for the holdback portion of a progress payment, with tax on the holdback generally becoming payable at the earlier of the day the holdback is actually paid out and the day it becomes payable under the contract — commonly once the applicable lien period has run — and that the recipient’s ability to claim an input tax credit on the same amount is generally tied to that same later timing rather than the original invoice date.
The practical consequence is that a construction ledger has two clocks in it, and a bookkeeping system that treats an invoice as a single taxable event will produce the wrong remittance on every draw. This is the single most common construction HST error, and it is structural rather than careless.
Section 240(1) requires every person who makes a taxable supply in Canada in the course of a commercial activity to be registered, except where the person is a small supplier, where the only commercial activity is supplying real property by way of sale otherwise than in the course of a business, or where the person is a non-resident not carrying on business in Canada. Section 148(1) defines the small supplier threshold by reference to consideration for taxable supplies in the four preceding calendar quarters not exceeding $30,000, or $50,000 for a public service body.
On the other side, tax paid on materials, subcontractor fees, equipment rentals and other taxable inputs is generally recoverable as an input tax credit — which is why the industry’s classic failure is a subcontractor who does not charge tax and a general contractor who consequently cannot recover it. Check it at onboarding rather than at year end.
Section 286(1) requires every person carrying on business or engaged in a commercial activity in Canada to keep all records necessary to determine their liabilities and obligations. Subsection (1.2) requires records to be kept in Canada in English or in French unless otherwise authorised; subsection (3) requires retention until six years after the end of the year to which they relate; subsection (3.1) requires records kept electronically to be retained in an electronically readable format for that period; and subsection (4) extends retention where the person objects or appeals, until the matter is finally disposed of.
The useful automation is on the evidence and the calendar, not the analysis. Extracting line items and tax amounts from supplier invoices so input tax credits reconcile to real documents; flagging a subcontractor invoice with no tax line and no registration number on file; recording substantial completion as a dated event and deriving the section 168(3) date from it; and separating holdback from the rest of the billing in the ledger so the two clocks stay distinct. Microsoft documents a prebuilt invoice model that extracts fields from invoices, which is the mechanical half of that work.
What software should not do is decide. Whether the work is substantially complete, whether a supply is zero-rated or exempt, whether a residential project triggers the self-supply rules, and what to file are decisions for an accountant who knows the contract. A model will answer all of them confidently and the confidence carries no information.
The following is illustrative — a composite of how the workflow is usually assembled, not a measured result.
A contractor in Ontario signs a written agreement for a commercial fit-out expected to run seven months — comfortably inside section 168(3)(c). It bills monthly, and each billing is split in the ledger into the payable portion and the holdback, with tax accounted for on the first at the earlier of payment and due date, and on the second on its own timing.
Substantial completion is recorded as a dated event when the consultant certifies it, and the system derives the outer date under 168(3) — the last day of the following calendar month — as a hard deadline for anything still unbilled. Nothing clever happened. A date that usually lives in someone’s head became a field, and the accountant reviewing the return had the contract, the certificate and the holdback schedule in one place.
Paragraph 168(3)(c) is framed around a supply under an agreement in writing for the construction, renovation, alteration or repair. If there is no written agreement the paragraph does not engage on its own terms, and you are back to the general rules in 168(1) and (2). That is a reason to have a written contract rather than a reason to avoid one.
Registration is not required while you are a small supplier, but registering allows you to claim input tax credits on materials and equipment. For a trade with significant material purchases the arithmetic often favours registering early. Confirm the position with an accountant, because it also brings filing obligations.
Not necessarily, but you must keep something that satisfies section 286 — kept in Canada, in English or French, retained six years after the end of the year to which the records relate, and in an electronically readable format if kept electronically. See automating receipt capture for how that works in practice, and the draw package article for how holdback appears on the billing side.
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