Every Ontario employer registered with WSIB is assigned a NAICS (North American Industry Classification System) code that determines their premium rate. This page explains how the classification system works, why it matters for your bottom line, and how to make sure you are in the right rate group.
The North American Industry Classification System is maintained by Statistics Canada, the U.S. Census Bureau, and Mexico's INEGI. It assigns every business a 6-digit code based on its primary economic activity. A residential framing contractor gets 238130. An electrician gets 238210. A trucking company gets 484110. WSIB uses these codes to group employers into rate groups — clusters of businesses with similar risk profiles and claims histories. Each rate group has a base premium rate expressed as dollars per $100 of insurable payroll. In 2025, rates range from as low as $0.28 per $100 (physicians) to as high as $6.78 per $100 (forestry and logging). The rate reflects the actual cost of injuries in that industry over the past several years — it is not arbitrary. Industries with frequent, severe injuries pay more because the claims cost more. The system is designed to be self-funding: premiums from all employers in a rate group collectively cover the cost of claims in that group.
Your NAICS code is the starting point for your entire WSIB cost. Get classified in the wrong group and you could be overpaying by thousands of dollars a year — or underpaying and facing a retroactive adjustment when WSIB audits your account. Here is a concrete example: a contractor who does mostly finish carpentry (trim, cabinetry, millwork) should be in NAICS 238350 at $3.87 per $100. If WSIB classified them as a framing contractor (238130) at $5.21 per $100, they would overpay by $1.34 per $100 of payroll. On $400,000 of insurable payroll, that is $5,360 per year in unnecessary premiums. The reverse is also true — if a roofing contractor is misclassified as a siding contractor, they are underpaying, and WSIB can retroactively reassess premiums with interest. When you register with WSIB, describe your business activities honestly and specifically. Do not say "construction" — say "residential renovation, primarily kitchen and bathroom remodels, 70% finish carpentry and 30% tile work." WSIB assigns the code based on your primary activity. If your business changes over time, request a reclassification review.
The base rate from your rate group is not your final premium. WSIB applies experience rating adjustments that reward employers with fewer claims and penalize those with more. For larger employers (premiums over $25,000), the MAP (Merit Adjusted Premium) program compares your claims costs against the rate group average. If your claims are lower, you get a discount — potentially up to 50% off the base rate. If your claims are higher, you pay a surcharge. For smaller employers, the SCIP (Safety Check Insurance Plan) offers a simpler binary assessment: meet basic safety requirements and get a rebate. The practical effect is significant. Two framing contractors in the same rate group with the same payroll can have premiums that differ by tens of thousands of dollars based purely on their claims history. This is why workplace safety is not just a legal obligation — it is a direct financial advantage. Every lost-time injury increases your experience rating surcharge for years. A single serious fall claim on a small contractor's account can increase premiums by 30% or more for 3 to 5 years.
Most industries in Ontario require mandatory WSIB registration. All of construction (NAICS 23), manufacturing (31-33), mining (21), transportation (48-49), retail (44-45), food service (72), and healthcare facilities (62) are mandatory. If you operate in these sectors and have employees, you must register with WSIB, report payroll, and pay premiums. Operating without coverage when it is mandatory is an offence under the Workplace Safety and Insurance Act — WSIB can retroactively assess premiums plus penalties. Some industries have optional coverage, primarily professional services (architects, engineers, consultants, lawyers, accountants) and certain financial services. Even in optional sectors, many employers choose to register because WSIB provides no-fault insurance: workers receive benefits without litigation, and employers are protected from negligence lawsuits. Independent operators — sole proprietors with no employees — can opt into WSIB coverage voluntarily. This is common in construction, where general contractors and principals require all subcontractors to provide WSIB clearance certificates regardless of the sub's employment status. Without coverage, the principal contractor inherits the liability for any workplace injury.
Construction has the widest spread of premium rates of any sector because the risk varies enormously by trade. At the high end, roofing contractors (238160) pay $6.24 per $100 — working at height on sloped surfaces with hot materials produces frequent and severe injuries. Structural steel and ironworkers (238120) pay $5.87 per $100 for similar reasons: falls from structural steel are among the deadliest workplace incidents in Ontario. Concrete foundation contractors (238110) pay $5.34 per $100 — formwork collapses, reinforcing steel injuries, and concrete pump accidents drive the claims. At the lower end of construction, electricians (238210) pay $2.78 per $100. Electrical work is hazardous in its own way (electrocution, arc flash), but the injury frequency is lower than trades involving heavy physical labour at height. Plumbers and HVAC contractors (238220) pay $2.95 per $100. Painters (238320) pay $3.21 per $100. These rates reflect real data: the trades with lower rates genuinely have fewer and less costly claims on average. That said, every trade carries risk, and the rates do not mean one trade is "safe" — they mean the aggregate cost of injuries across all employers in that code is lower per dollar of payroll.
Type your trade, job description, or NAICS code number into the search bar. The tool instantly filters all entries and shows matching NAICS codes with their WSIB rate group, base premium rate per $100, mandatory or optional coverage status, and common trade names that fall under each code. You can also browse by NAICS section using the filter pills — useful if you are not sure which code applies and want to scan all construction codes, for example. The rates shown are 2025 base rates before experience rating adjustments. Your actual premium will differ based on your MAP/SCIP adjustment, claims history, and insurable earnings. Use the print button to generate a PDF of your search results for your records or to share with your accountant. For your specific rate, contact WSIB at 1-800-387-0750 or log into your account at wsib.ca.