Understanding WSIB Premiums in Ontario

The Workplace Safety and Insurance Board (WSIB) provides no-fault workplace injury insurance for Ontario employers. Under the Workplace Safety and Insurance Act (WSIA) 1997, most employers are required to register, report insurable earnings, and pay premiums. Your premium rate depends on your industry classification and your claims track record.

How WSIB premiums are calculated

The formula is straightforward: take your total insurable payroll, divide by $100, and multiply by your premium rate. The premium rate is set by WSIB for each NAICS (North American Industry Classification System) rate group and reflects the historical injury costs in that industry. A framing contractor pays $9.12 per $100 because framing has a higher injury frequency and cost than, say, professional services at $0.36 per $100. Each worker's earnings are capped at the maximum insurable amount — $112,500 for 2025 — meaning you do not pay premiums on earnings above that threshold per worker. Insurable earnings include regular wages, overtime, vacation pay, bonuses, commissions, and the value of board and lodging provided. They do not include employer-paid benefits like health insurance or pension contributions, nor do they include tips that the employer does not control. For a small residential construction company with 5 workers averaging $65,000 per year, the math works out to: ($325,000 / $100) x $5.66 = approximately $18,395 per year, or about $1,533 per month. That is the base premium before any experience rating adjustment.

NAICS rate groups and why your code matters

WSIB assigns every employer to a rate group based on their NAICS code — the 4-to-6-digit industry classification that describes what their business does. The rate group determines your base premium rate. Within construction alone, rates range from $2.49 per $100 for electrical contractors to $9.12 for framing contractors. This spread reflects real differences in injury frequency and severity. Roofers and framers sustain more lost-time injuries per thousand workers than electricians or sheet metal workers. If your business spans multiple activities, WSIB classifies you based on your predominant activity. A general contractor who does their own framing will likely be classified under residential building construction (23611) at $5.66, not under framing (23835) at $9.12 — but this depends on your specific WSIB assessment. Getting classified into the wrong rate group can cost thousands per year. Review your NAICS code on your WSIB statement of account and contact WSIB if it does not match your primary business activity.

Experience rating: how your claims history raises or lowers your premium

The base rate is just the starting point. WSIB adjusts your premium up or down through experience rating, which compares your actual claims costs to what is expected for your rate group. Under the current Rate Framework, larger employers are assessed through the Merit Adjusted Premium (MAP) plan, while smaller employers may fall under the Safety Check for Independent Practice (SCIP) program. The principle is the same: if your workplace generates fewer or less costly claims than the average employer in your rate group, you pay less. If your claims are worse, you pay more. The adjustment can be significant — a well-run contractor with no lost-time claims might earn a 30% to 40% rebate, while a contractor with a string of serious claims could face a 50% to 100% surcharge. For a business paying $18,000 in base premium, a 30% rebate saves $5,400 per year; a 50% surcharge adds $9,000. This is why return-to-work programs, safety training, and hazard prevention are not just legal obligations — they are direct cost controls. Every lost-time claim stays on your record for multiple years, affecting your experience rating long after the worker has returned.

The maximum insurable earnings cap

WSIB sets a maximum insurable earnings amount each year. For 2025, the cap is $112,500 per worker. If a worker earns $140,000, you only pay premiums on $112,500 of that. The cap also limits the worker's benefits if they are injured — their loss-of-earnings benefits are calculated on the capped amount, not their full salary. The cap is indexed and typically increases each year based on average industrial wage growth in Ontario. For most trades workers and construction labourers, annual earnings fall below the cap. It becomes relevant for project managers, senior estimators, supervisors, and highly skilled tradespeople working significant overtime. When estimating premiums, always check whether your workforce includes anyone above the cap — it can make a meaningful difference in the total premium for smaller crews with high earners.

Clearance certificates and subcontractor liability

One of the most expensive mistakes a general contractor or principal can make is failing to obtain a WSIB clearance certificate from a subcontractor before paying them. Under WSIA section 141, if a subcontractor does not have WSIB coverage and one of their workers is injured on your project, you — the principal contractor — inherit liability for the sub's WSIB premiums and claims costs. A clearance certificate is a letter from WSIB confirming the sub is registered, has reported earnings, and is in good standing. It is free to request and takes minutes to verify online through WSIB's e-Clearance system. Make it a non-negotiable condition of every subcontract: no clearance certificate, no payment. The cost of one uninsured subcontractor claim can dwarf years of your own premium payments.

Reporting obligations and payment schedule

WSIB premiums can be paid monthly, quarterly, or annually depending on your premium size. Most small to mid-size employers pay monthly through the Premiums Reporting system. You report your actual insurable earnings each period, and WSIB calculates the premium due. Underreporting earnings is a serious offence — WSIB audits employer payroll records and compares them to CRA filings. If they find unreported earnings, you will owe back premiums plus penalties and interest. At year-end, you file a reconciliation showing total actual insurable earnings for the year. If your reported amounts through the year were too low, you owe the balance. If too high, WSIB credits the overpayment. New employers pay a deposit equal to approximately two months of estimated premiums when they first register. Workplace injuries must be reported on Form 7 (Employer's Report of Injury/Disease) within 3 business days of learning about any injury that requires health care or causes lost time. Late or missing Form 7s can result in penalties and negatively affect your experience rating.