In Ontario, fault after a car accident is decided by your own insurance company using a fixed set of diagrams and scenarios in Regulation 668 under the Insurance Act, known as the Fault Determination Rules.1Ontario.ca. R.R.O. 1990, Reg. 668 – Fault Determination Rules Every licensed insurer in the province has to apply the same rules the same way, and the percentage of fault they assign you (usually 0%, 50%, or 100%) controls what you pay out of pocket, what happens to your premium, and whether you can sue the other driver.
Who Decides Fault and How
Fault is decided by an adjuster at your own insurance company, not by police and not by a court. The adjuster reads the facts of the collision and matches them to the closest scenario in Regulation 668. The regulation is organized by crash type — rear-end, lane change, intersection, parking lot, driveway, chain reaction, and so on — and each scenario comes with a predetermined fault split. Even if the circumstances feel unusual, the adjuster is required to find the rule that most closely fits.
Police do something different. They respond to the scene to decide whether anyone broke the Highway Traffic Act, which can lead to a ticket, demerit points, or a court summons.2Ontario.ca. Highway Traffic Act, R.S.O. 1990, c. H.8 That process has no formal bearing on fault for insurance purposes. A driver can be charged with careless driving and still carry 0% fault under Regulation 668. A driver who walks away without a ticket can still be found 100% at fault by their insurer. The two systems ask different questions.
How Common Accidents Are Scored
Rear-End Collisions
If you hit the car in front of you, you are 100% at fault.3Ontario.ca. R.R.O. 1990, Reg. 668 – Fault Determination Rules – Section 6 It doesn’t matter if the lead car stopped suddenly, if the road was icy, or if traffic was unpredictable. The rule treats keeping a safe following distance as entirely the trailing driver’s responsibility. Arguing that the car ahead braked without warning almost never changes the outcome.
Lane Changes and Sideswipes
A driver who moves into another lane and hits a vehicle already traveling in it is 100% at fault.4Ontario.ca. R.R.O. 1990, Reg. 668 – Fault Determination Rules – Section 10 The regulation assumes the car already in the lane had right of way. For sideswipes, the position of each vehicle relative to the lane markings decides who crossed into whose space.
Left Turns at Intersections
A driver turning left across oncoming traffic who gets hit by a vehicle going straight through is 100% at fault, unless the oncoming vehicle ran a red light or a stop sign.5Ontario.ca. R.R.O. 1990, Reg. 668 – Fault Determination Rules – Section 12 Proving the other driver ran the signal usually takes dashcam footage or a credible independent witness. Without that, the left-turning driver carries full liability.
Parking Lots
Parking lots have their own section.6Ontario.ca. R.R.O. 1990, Reg. 668 – Fault Determination Rules – Section 16 The main driving lanes through a lot (called thoroughfares) are treated like regular roads, so vehicles already on them have right of way. A driver pulling out of a parking space, or coming from a smaller feeder lane, who fails to yield to traffic on a thoroughfare is 100% at fault. Many drivers assume parking lots are a free-for-all; they aren’t.
Driveways and Private Roads
A driver pulling onto a public road from a private driveway or private road is 100% at fault if they hit a vehicle already on that road, as long as no traffic signals control the spot.7Ontario.ca. R.R.O. 1990, Reg. 668 – Fault Determination Rules – Section 7 If you are turning left into a driveway and get hit by a car trying to pass you from behind, fault splits 50/50. But if the passer went around multiple cars that were stopped behind you waiting, the passer carries 100%.
Chain Reactions and Pileups
In a same-lane chain reaction with three or more vehicles, each pairwise collision gets assessed on its own.8Ontario.ca. R.R.O. 1990, Reg. 668 – Fault Determination Rules – Section 9 If three cars are moving (A ahead, B in the middle, C at the rear) and all collide, B is 50% at fault for hitting A, and C is 100% at fault for hitting B. If only the rear car was moving and shoved B into A, C is fully at fault and neither A nor B bears any fault for their own contact.
For pileups across adjacent lanes, the rule is blunter: each driver involved in a collision with another vehicle is assigned 50% fault.9Ontario.ca. R.R.O. 1990, Reg. 668 – Fault Determination Rules – Section 11 In a multi-lane pileup it is usually impossible to tell who drifted first.
How the Percentages Are Decided
Most assessments land at a clean 0/100 split. Shared liability happens, but it isn’t the default some drivers expect. If two different rules apply to the same driver, the insurer must use the one that assigns the least fault.10Ontario.ca. R.R.O. 1990, Reg. 668 – Fault Determination Rules – Section 4 The one exception: if one applicable rule puts the driver at 100% and another puts them at 0%, the result defaults to 50%.
When no diagram in the regulation matches the collision, the insurer doesn’t fall back on a reflexive 50/50. Fault gets decided under the ordinary rules of law, meaning general negligence principles apply as if Regulation 668 didn’t exist.11Ontario.ca. R.R.O. 1990, Reg. 668 – Fault Determination Rules – Section 5 The same approach is used when there isn’t enough evidence to figure out what happened.
Any fault above 0% means the crash is recorded on your driving history as an at-fault accident. That single line on the record drives everything that follows.
What a Fault Finding Costs You
Your Deductible and What Your Insurer Pays
Property damage to your own car is handled under Direct Compensation–Property Damage, a mandatory piece of every Ontario auto policy. Your fault percentage decides what your insurer pays. If you are found 50% or more at fault, your insurer pays only 50% of your loss after your deductible is subtracted.12Financial Services Regulatory Authority of Ontario. After an Accident – Understanding the Claims Process At 0% fault, your insurer covers the full loss and no deductible applies. On a moderate collision, the gap between a 0% and 50% finding can run into thousands of dollars.
Your Premium
A collision where you are assigned 50% or more fault typically pushes premiums up 20% to 50% at renewal, and more for drivers already classified as high risk. The sharpest increases hit in the first two or three years and taper off if you stay claim-free and conviction-free. Depending on the insurer, the at-fault accident can sit on your record for six years or longer.
Ontario builds in one piece of protection for small crashes. If an at-fault collision caused less than $2,000 in total damage, involved no injuries, and no claim payout was made, your insurer cannot raise your premium. This protection applies to one minor collision every three years. Some insurers also sell an accident forgiveness endorsement that blocks a premium increase after your first at-fault collision. It has to be on the policy before the accident, it only covers the primary listed driver, and it does not apply if the collision involved impaired driving or another Criminal Code offence.
When You Can Still Sue the Other Driver
Ontario’s no-fault system limits lawsuits against the at-fault driver, but it doesn’t shut them down entirely. You can sue for pain and suffering if your injuries meet the legal threshold: a serious and permanent impairment of an important bodily function. In practice, that means injuries that stop you from working, caregiving, or carrying out daily life for the foreseeable future. If you recovered within a year and got back to your pre-accident life, courts rarely find the threshold met.
Even past the threshold, a statutory deductible applies to pain and suffering awards. For 2025, the deductible was $46,790.05, subtracted from any pain and suffering award below $155,965.54.13Financial Services Regulatory Authority of Ontario. 2025 Automobile Insurance Indexation Amounts Guidance Awards above that higher figure are paid in full. Both numbers are indexed yearly, so the 2026 amounts will be slightly higher once FSRAO publishes them. The deductible is why smaller pain and suffering awards can be reduced to almost nothing, and why many lawyers won’t take on a case unless the injuries are clearly severe.
Disputing a Fault Decision
Start With Your Insurer
Ask your adjuster for a written explanation of exactly which section of Regulation 668 was applied. Dashcam footage, high-resolution photos of the vehicles and the scene, and written statements from independent witnesses can sometimes prompt a reassessment. If the adjuster won’t move, every licensed insurer in Ontario is required to have an internal complaint process, and you can escalate to the company’s ombudsman or senior complaints officer.14Financial Consumer Agency of Canada. How to File a Complaint About Your Insurance Company
Outside Review
If internal escalation goes nowhere, the General Insurance OmbudService is an independent body that handles unresolved complaints about auto, home, and business insurance across Canada.14Financial Consumer Agency of Canada. How to File a Complaint About Your Insurance Company It offers mediation and can help determine whether your insurer applied Regulation 668 correctly.
You can also complain to the Financial Services Regulatory Authority of Ontario, the provincial regulator for auto insurance. FSRAO can investigate whether the insurer followed the rules, but it cannot settle your dispute, order a refund, or award compensation.15Financial Services Regulatory Authority of Ontario. Submit a Complaint to FSRA If the dispute is really about entitlement to Statutory Accident Benefits rather than fault, that goes to the Licence Appeal Tribunal instead.
Court
As a last resort, you can sue and ask a judge to decide liability. Courts aren’t bound by Regulation 668 and can apply ordinary negligence principles to reach a different result. Watch the clock. Ontario’s Limitations Act sets a basic two-year limitation period from the date you discovered the claim.16Ontario.ca. Limitations Act, 2002, S.O. 2002, c. 24, Sched. B – Section 4 For auto insurance claim denials specifically, the Insurance Act may impose a shorter one-year window from the date of loss. The timing can get complicated by when you actually learned the insurer was denying your claim versus the accident date, so treating two years as a hard outer boundary is the safer move.