Silo 1 · Global Late Payment Law

Calculating Late Interest Under Canadian Laws
2026 Legal Guide

By Santanu Sarma — Economics Honors, Bhattadev University · Updated June 2026 · 13 min read

Picture this: you're a brand designer based in Vancouver. A mid-sized marketing agency hired you to overhaul their client's visual identity — a substantial project, solid brief, clear deliverables. You delivered everything on time and on budget. The invoice was $4,500 CAD, net-30. Then net-30 became net-60. Then their AP team started sending you a rotating cast of excuses.

When the agency finally paid — 90 days late, and only after three increasingly firm emails — they paid the principal. Just the principal. No late fee, despite the fact that your invoice clearly stated "2% per month on overdue balances." When you pushed back, they said the clause was unenforceable. You didn't believe them, so you took it to small claims court in British Columbia.

The adjudicator agreed with them. Not because your late fee was unreasonable. Not because you hadn't communicated it clearly. But because of five words missing from your invoice — words that, under Section 4 of the federal Interest Act, caused the court to automatically substitute your stated 2% monthly rate with the statutory default of 5% per annum. Instead of recovering $270 in late fees, you recovered $55. Court costs ate the rest.

This scenario plays out in small claims courts across Canada every year. It is the single most preventable invoicing mistake in the country, and it costs Canadian freelancers and small businesses thousands of dollars annually in otherwise valid, legally enforceable penalty claims. This guide explains exactly what the Interest Act trap is, how to avoid it in five seconds, and everything else you need to know about charging late fees in Canada legally and effectively.

The Interest Act Trap: Section 4 Explained

The federal Interest Act, R.S.C. 1985, c. I-15, is a short statute — fewer than 20 sections — but Section 4 is a trap that catches an enormous proportion of Canadian freelancers and small business owners who try to charge late payment interest.

Section 4 reads, in plain terms: whenever interest is payable at a rate or percentage per day, week, month, or any period shorter than a year, and the contract or document does not express the equivalent yearly rate or percentage of such interest, no interest exceeding 5% per annum shall be chargeable, payable, or recoverable.

That is not a penalty. It is not a reduction. It is a complete substitution. The court does not say "we'll give you something less than 2% per month." It says "you get 5% per annum and nothing more, because you didn't write the annual rate on the document."

Why This Catches So Many People

The mistake is intuitive to make. "1.5% per month" feels perfectly clear — any reasonable adult can multiply by 12 and get 18%. But Section 4 does not care what a reasonable adult can calculate. It requires that the annualized rate appear explicitly on the same document as the periodic rate. The reader does not need to do the math; the document must do it for them.

Standard invoice templates downloaded from the internet almost universally get this wrong. They include a monthly late fee percentage field with no annual equivalent. If you've been using one of those templates, every late fee clause on every invoice you've sent in Canada has been legally uncollectable at the rate you intended — and you may not have known it.

The Exact Wording That Fixes It

The correction requires no legal drafting skill. Add one parenthetical to your late fee clause. These formulations are legally compliant under Section 4:

The annualized rate must appear on the same document — the invoice itself, your standard terms if incorporated by reference into the invoice, or your client agreement. A website link that the client might find if they clicked around is insufficient. Put it directly on the invoice.

What Rate Should You Use?

There is no provincially mandated B2B rate in Canada — unlike the UK or the EU, Canadian law does not impose a statutory interest rate on overdue commercial invoices. You are free to set whatever rate you and your client agree to, subject to two constraints: the Section 4 disclosure requirement and the Criminal Code ceiling discussed below.

The industry standard settles at 18% to 24% per annum (1.5% to 2% per month) for a practical reason: these rates are high enough to create a genuine incentive to pay on time, low enough to be commercially defensible, and far enough below the criminal ceiling to avoid any legal jeopardy.

Worked Example: $4,500 CAD Invoice, 45 Days Overdue

This is the same scenario from the introduction — but this time, the invoice has the correct Section 4 wording: "1.5% per month (18% per annum)." Here is what you can legally recover.

Method 1 — Using the Monthly Rate Directly

Method 2 — Using the Annual Rate with Exact Day Count (Recommended for Claims)

On a single $4,500 invoice, the difference between compliant and non-compliant wording is $72. On a $25,000 invoice overdue for 60 days, that same gap — between 18% p.a. and the 5% p.a. default — becomes $499 vs $205: a difference of nearly $300. Multiply that across a year of invoicing and it's a meaningful number.

The Criminal Code Ceiling: 35% APR

While the Interest Act sets a disclosure trap at the low end, the Criminal Code of Canada sets an absolute ceiling at the high end. Section 347 of the Criminal Code makes it a criminal offence to enter into an agreement or arrangement to receive interest at a criminal rate — and to receive payment or partial payment of interest at that rate.

In 2023, Bill C-26 amended Section 347 to modernise the criminal rate definition. The current threshold is 35% APR (Annual Percentage Rate), replacing the previous standard which had been interpreted as approximately 60% effective annual rate using compound calculations. The 35% APR figure is calculated on an annual basis using standard APR methodology — it is not an effective annual rate that can be gamed through monthly compounding.

Why This Matters for Freelancers

In practice, no reasonable freelancer or small business comes anywhere near this ceiling — 35% APR is well above anything commercially justifiable for a standard invoice late fee. But understanding where the ceiling sits explains why 18% to 24% per annum has become the industry standard: it sits comfortably below the criminal threshold, signals commercial seriousness, and is defensible as a genuine pre-estimate of the cost of late payment.

Where the ceiling becomes practically relevant is for anyone tempted to use aggressive penalty escalation clauses — for example, a clause that doubles the late fee rate every 30 days, or imposes compound interest on unpaid late fee balances. These structures can cross the 35% APR line faster than they appear to on a monthly rate basis. If you are considering anything beyond a standard flat monthly rate, have a commercial solicitor or lawyer check it before it goes on your invoices.

The Safe Band: 18% to 24% Per Annum

The sweet spot for Canadian B2B late fees is 18% to 24% per annum. Below that band, you're not creating a sufficient incentive for timely payment — a client who can borrow at prime plus 3% from their bank has no rational reason to pay your invoice on time if you're only charging 8% per annum on late balances. Above 24%, you start moving into territory that requires more justification in court, even if you're still comfortably below the criminal ceiling.

Most standard Canadian business invoice templates and accounting software defaults (FreshBooks, QuickBooks Canada, Wave) pre-populate late fee fields at 1.5% per month (18% per annum) — and now you know exactly why.

Do You Need a Signed Contract to Charge Late Fees?

The short answer is no — but "no" comes with important qualifications that determine whether your late fee clause will actually hold up if challenged.

Canadian courts have upheld late fee claims in the absence of a formally signed contract, provided the late fee terms were clearly communicated to the client before or at the commencement of the commercial relationship. The key test is notice: did the client have a reasonable opportunity to know about and accept the late fee terms before they engaged your services?

What Counts as Sufficient Notice

Courts in Ontario, British Columbia, and Alberta have found adequate notice where the late fee terms appeared in a proposal document accepted by email, in standard terms incorporated by reference into a quote, on an invoice that the client signed or responded to without objection, or in a client onboarding email that included the terms and received an acknowledgment. The common thread is that the client received the terms and had a real opportunity to object before the work began.

What Does Not Work

Adding a late fee clause for the first time on an overdue invoice does not create a retroactive entitlement. The client never agreed to the terms — they existed only after the debt was already in dispute. Similarly, terms buried in a footer in 6-point font on a document where everything else is 11-point have been found insufficient where the court concluded the client had no reasonable notice they were accepting additional financial obligations.

The Practical Best Practice

Include your late fee clause — with the Section 4-compliant annual rate disclosure — in your initial client proposal or engagement letter. Have the client acknowledge it by email or signature. Repeat the clause on every invoice. This three-step approach creates an airtight evidentiary record that the terms were accepted before the work started and were consistently applied throughout the relationship.

Provincial Prompt Payment Acts: Construction and Trades

If your work falls within the construction and skilled trades sector, a separate layer of law applies on top of the general Interest Act framework — and in some provinces, it overrides standard contractual payment terms entirely.

Several Canadian provinces have enacted dedicated Prompt Payment legislation that mandates specific payment timelines in construction contracts, regardless of what the parties agreed. These are not suggestions or defaults — they are statutory minimums that cannot be waived by contract.

Ontario: Construction Act (2019)

Ontario's Construction Act, as substantially amended in 2019, requires owners to pay contractors within 28 days of receiving a proper invoice, and contractors to pay subcontractors within 7 days of receiving payment from the owner. Late payment under the Act triggers mandatory interest at the rate prescribed by regulation — currently set at the Bank of Canada overnight rate plus 1%, compounded monthly. The Act also creates adjudication as a rapid dispute resolution mechanism, allowing unpaid contractors to obtain a binding interim decision within 30 days without going to court.

Alberta: Prompt Payment and Construction Lien Act (2022)

Alberta's legislation, which came into force in August 2022, follows a similar framework: a 28-day payment window for owners-to-contractors and a 7-day window for contractors-to-subcontractors. Interest on late payments accrues at the prescribed rate from the day after the payment was due. The Act also includes mandatory adjudication for payment disputes.

Saskatchewan and British Columbia

Saskatchewan enacted its Prompt Payment for Construction Act, which came into force in February 2022, with substantially similar 28-day and 7-day payment windows and adjudication rights. British Columbia passed its prompt payment legislation as part of the Builders Lien Act amendments, with staged implementation — the prompt payment provisions are now in effect for most construction contracts in the province.

If you work in construction or skilled trades in any of these provinces, check whether your contract is subject to the provincial Prompt Payment Act — the mandatory timelines and statutory interest provisions may give you stronger and faster remedies than your contractual late fee clause.

Cross-Provincial Considerations: Which Law Applies?

The Interest Act is federal law and applies uniformly across all provinces and territories. The Section 4 annualization requirement and the Criminal Code Section 347 ceiling apply to every commercial invoice in Canada, regardless of where either party is located.

Provincial variation enters in two ways: prompt payment legislation (discussed above, applicable only in provinces that have enacted it, and primarily in the construction sector) and provincial court procedures for enforcing late payment claims.

Small Claims Limits by Province

If you need to enforce a late payment claim through the courts, the monetary limit of the Small Claims Court (or its equivalent) varies by province. In Ontario, the limit is $35,000. In British Columbia, it is $35,000. In Alberta, $50,000. In Quebec, the Court of Québec's Small Claims Division handles claims up to $15,000 for individuals but not for businesses — business claimants in Quebec go to the Civil Division for amounts above $15,000. For amounts above your province's small claims limit, you'll need to file in the superior court, and legal representation becomes practically necessary.

Choice of Law in Cross-Provincial Contracts

Where you and your client are in different provinces, your contract's governing law clause determines which province's procedural rules apply. The substantive federal Interest Act and Criminal Code provisions apply regardless. If your contract has no governing law clause — common in informal freelance engagements — courts typically apply the law of the province where the services were primarily performed.

How to Actually Collect: Issuing a Formal Late Payment Demand

Knowing your rights under the Interest Act and the Criminal Code ceiling is necessary but not sufficient. You also need to know how to convert that knowledge into actual recovered money. The process for most B2B late payment situations is a formal demand letter, not an immediate court filing.

Step 1 — Verify Your Invoice Is Section 4-Compliant

Before sending any formal demand, confirm that the invoice in question — and your standard terms, if incorporated by reference — contains the annualized rate disclosure. If it doesn't, you cannot credibly demand interest above 5% per annum. This is not a reason to give up; it is a reason to correct your template for every future invoice and to claim at 5% for the current one while acknowledging the disclosure gap.

Step 2 — Calculate Using the Annual Rate and Day Count

Use the formula I = P × r × (days ÷ 365) with the annualized rate from your invoice. Document the calculation with the invoice reference, the due date, the payment date (or today's date if still outstanding), the rate used and its source (your invoice terms), and the daily accrual figure. Precision matters — a clean calculation that shows your work is much harder for a debtor to dispute than a round number with no supporting arithmetic.

Step 3 — Send the Formal Demand

Address the demand to the company's Finance Director or Controller — not your day-to-day contact. Cite the invoice reference, the original due date, the number of days overdue, your contractual late fee rate (with the annual equivalent), the calculated interest, and a total amount due. Give a clear 14-day payment deadline. Send by email with read receipt and by courier or registered mail to their registered business address. Dual delivery creates a clean evidentiary record if the matter proceeds to court.

Step 4 — Small Claims If Ignored

If no payment is received within the deadline, file in your province's Small Claims Court (or equivalent). The filing fees are modest, the process is designed for self-represented claimants, and a judgment — once obtained — can be enforced against the debtor's bank accounts and assets. Most commercially rational debtors settle before the hearing date once they receive the Statement of Claim.

The Bigger Picture: Five Words That Changed Everything

The entire Section 4 problem reduces to five words: "(18% per annum)" or "(24% per annum)" appended to your monthly rate. That is the fix. It takes five seconds to add to an invoice template and precisely zero additional legal expertise to implement.

The reason this matters beyond the individual claim is behavioral. A client who knows your invoices contain properly disclosed, legally enforceable late fees — and who has once seen you actually calculate and claim them — treats your payment terms differently than a client who assumes you're just another freelancer who will send polite chasers indefinitely.

The financial return on fixing your invoice template is not just the interest you recover on the next late payment. It's the invoices that start clearing on day 28 instead of day 72 from the moment clients understand you enforce.

And for any Canadian freelancer running a portfolio of clients — five to ten active projects, monthly invoicing, a mix of prompt and slow payers — a systematic approach to late fee documentation and enforcement compounds into a meaningful annual number. At 18% per annum, a client who habitually pays a $6,000 monthly invoice 40 days late is generating $118.36 per invoice in recoverable late interest — over $1,400 per year on a single client relationship, every dollar of which is yours under Canadian law. You just have to write the annual rate on the invoice.

Frequently Asked Questions

This article is informational and reflects the federal Interest Act (R.S.C. 1985, c. I-15), Criminal Code Section 347 as amended by Bill C-26 (2023), and provincial Prompt Payment legislation as of June 2026. It is not legal advice. Provincial court limits, prompt payment thresholds, and prescribed interest rates are subject to change — verify all figures with the relevant provincial authority or a licensed Canadian lawyer before relying on them for a specific claim or court filing.