Late Expert Reports in Ontario Personal Injury Litigation: Rules 53.03 and 53.08
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Ontario changed the rules governing late expert evidence on March 31, 2022.
Before the amendment, Rule 53.08 stated that leave to introduce evidence affected by procedural non-compliance “shall” be granted on just terms, with an adjournment if necessary, unless admission would cause prejudice or undue trial delay. The former wording placed the emphasis on whether the consequences of late service could be cured.
Ontario Regulation 18/22 replaced that approach. Under the amended Rule 53.08, leave “may” be granted only if the party responsible for the failure satisfies the judge that:
there is a reasonable explanation for the failure; and
granting leave would not cause prejudice that cannot be compensated through costs or an adjournment, or cause undue delay in the conduct of the trial.
The amendment shifted the burden to the party seeking permission to rely on the late evidence, made a reasonable explanation an express requirement and gave judges greater discretion to refuse leave. The absence of identifiable prejudice is no longer necessarily enough.
The expert-report deadlines themselves did not change. Rule 53.03 requires that an initial expert report at least 90 days before the pre-trial conference and a responding report at least 60 days before it. What changed on March 31, 2022 was the test applied when those requirements are not met.
The decisions since the amendment have examined when inadvertence can provide a reasonable explanation, whether a report is initial or responding, how service after the pre-trial conference affects the analysis and when prejudice or trial disruption requires exclusion.
In serious personal injury litigation, Ontario personal injury lawyers must identify the medical, vocational, economic and future-care evidence needed to prove the claim early enough to comply with the Rules. A crucial report could be excluded even if the trial remains months away if the party responsible for the default cannot adequately explain it.
Why Rule 53.08 Changed on March 31, 2022
The amendment to Rule 53.08 formed part of a broader reform of Ontario’s pre-trial and expert-evidence procedures.
The Civil Rules Committee identified the objective as reducing the number of trials which are adjourned because expert evidence was delivered too late. The related amendments were designed to ensure that the expert case was substantially developed before the pre-trial conference, allowing meaningful settlement discussions and informed trial-management decisions.
Several related changes came into force on March 31, 2022. Rule 50.03.1 introduced a certificate of readiness that each party must deliver at least 30 days before the pre-trial conference. A party who intends to call expert evidence must identify whether each report was served within the Rule 53.03 deadline and, where it was not, provide the reason.
The March 31, 2022 amendment therefore changed more than a single word. Moving from “shall” to “may,” adding the reasonable-explanation requirement and shifting the burden to the defaulting party altered the starting point for admissibility.
The Rule 53.03 Expert-Report Timetable
Rule 53.03 of the Rules of Civil Procedure establishes the primary deadlines. Parties who intended to call an expert witness at trial must serve the expert’s signed report at least 90 days before the pre-trial conference. A party intending to call an expert in response must serve the responding report at least 60 days before the conference.
Supplementary reports are tied to the trial date. A supplementary report setting out additional proposed testimony must be served at least 45 days before trial. Responding supplementary reports need to be served at least 15 days before trial.
Those later periods do not provide an opportunity to complete an expert case that should have been developed prior to the pre-trial conference. Whether a report is genuinely supplementary depends on its substance, as opposed to its label. A report from a new discipline addressing an issue that has existed throughout the action will not become supplementary simply because its called a supplementary report.
Whether Rule 53.03 applies to a treating professional or another witness is a separate threshold question. Ontario courts distinguish opinions formed through treatment or participation from opinions later developed for litigation, as discussed in our analysis of participant experts in Ontario personal injury litigation.
What Changed in the Test for Late Expert Evidence?
Under the former Rule 53.08, leave was presumptively available unless admission would cause prejudice or undue trial delay. Adjournments could be utilized if where necessary to permit the opposing party to respond.
The amended rule reverses that orientation. The party responsible for the default must satisfy the judge that:
the failure has a reasonable explanation; and
admitting the evidence would not cause non-compensable prejudice or undue trial delay.
Both requirements must be established. The importance of the report and the absence of obvious prejudice do not eliminate the requirement for a reasonable explanation.
Even if both requirements are met, the use of “may” rather than “shall” preserves judicial discretion. Rule 53.08 does not require leave to be granted merely because the two express requirements have been addressed.
The msost well known early application of the new regime was Agha v. Munroe, 2022 ONSC 2508.
When the jury trial commenced, the plaintiff had no expert reports addressing past or future income loss, rehabilitation needs or housekeeping expenses. Counsel relied on the cost of obtaining the reports and proposed commissioning opinions during the trial.
Leave was refused. The financial explanation was not accepted as reasonable, and reports prepared after trial had begun would have deprived the defendants of a fair opportunity to respond and risked an adjournment or mistrial.
While Agha was an extreme scenario, commentary in the decision by Justice Edwards made it clear that that late expert evidence would no longer be routinely accepted. That decision established a strict starting point, but the cases that followed show that the amended rule must still be applied to the full procedural history.
Initial and Responding Expert Reports After Harris
The distinction between what constitutes an initial report and a responding report turns on the report’s function and the sequence of the evidence. It is not determined solely by which party bears the ultimate burden of proof.
An interesting application of this was rule was in Harris v. Prescott, 2026 ONSC 240 (Div. Ct.), the plaintiffs alleged that a hospital had failed to provide adequate supervision and care after a patient was sexually assaulted by a visitor while in hospital.
The action was set down for trial without the parties establishing the expert-report schedule required by Rule 53.03(2.2). More than nine months later, the hospital served a nursing standard-of-care report without previously advising the plaintiffs that it intended to obtain that evidence.
The plaintiffs retained a nursing expert in response and served their report two weeks after the 60-day deadline. The motion judge treated the plaintiffs’ report as an initial report governed by the 90-day deadline because the plaintiffs bore the burden of proving negligence.
The Divisional Court held that this was an error. The hospital had served the first nursing report, and the plaintiffs’ report responded to it. The 60-day deadline therefore applied.
The court also considered:
the parties’ failure to establish the required expert timetable;
the unexpected delivery of the hospital’s report;
the plaintiffs’ prompt effort to obtain responding evidence;
the comparatively brief delay;
the absence of prejudice; and
the lack of danger to the trial date.
Harris confirms that the amended rule is not applied by looking at the missed date in isolation. The court must identify the role of the report and assess the explanation within the procedural history that produced the default.
The decision does not restore the former presumption in favour of admission. It shows that the stricter post-2022 test remains contextual and should not be used to exclude a prompt response to an unforeseen report merely because the calendar was not met.
What Is a Reasonable Explanation Under Rule 53.08?
A reasonable explanation must justify the failure when assessed against the purpose of the expert timetable.
The court will ordinarily consider:
when the need for the evidence became apparent;
when the expert was contacted and retained;
when the necessary records and instructions were supplied;
what follow-up occurred;
when the default was discovered;
how quickly the party responded; and
whether any part of the delay was strategic.
The unexpected death, retirement or unavailability of a retained expert may provide a reasonable explanation for a replacement report. The moving party must still explain the steps taken after the problem arose and establish that the unexpected event caused the delay affecting the particular report.
By contrast, postponing a report in the hope that the action will settle, the opposing party will abandon an issue or the expense can be avoided is difficult to reconcile with Rule 53.03. Expert evidence is intended to inform the pre-trial process, not be commissioned only after that process fails to produce a settlement.
When Can Inadvertence Excuse a Late Expert Report?
The post-2022 decisions do not establish that inadvertence is always sufficient or always insufficient as it depends on a detail explanation. A clearly explained calendaring or administrative error could poentially satisfy Rule 53.08. However, a lengthy period of inactivity cannot be converted into a reasonable explanation merely by describing it as inadvertent.
In Quinn v. Rogers, 2024 ONSC 1967, three responding reports were served 19 days late because counsel mistakenly believed the pre-trial conference was scheduled for later in the month.
Two reports had already been completed within the required period. Counsel accepted responsibility through affidavit evidence and offered the plaintiffs sufficient time to obtain replies.
The court accepted the calendaring error as a reasonable explanation and extended the deadline.
In Seo v. Francis, 2024 ONSC 4341, the explanation involved staff turnover, different lawyers handling the file and personal difficulties experienced by counsel. The reports had been served prior to the pre-trial conference. The court characterized the explanation as being at the low end of reasonableness but granted relief in the circumstances.
These decisions demonstrate that a defined and limited error may be accepted where the reports exist, the default is addressed promptly and the purposes of the pre-trial conference have not been defeated.
Kasongo: Inadvertence Accepted on a Detailed Record
In Kasongo v. Stanley, 2026 ONSC 2731 the plaintiff served a future-care-cost report 34 days before the pre-trial conference rather than the required 90 days. The report collected and priced treatment recommendations contained in previously served medical evidence. Trial was still approximately 14 months away.
Counsel had diarized the deadline and instructed an experienced law clerk to arrange the report but did not follow up during a busy period. Once the omission was discovered, the report was commissioned and served within approximately one month.
The court accepted the explanation on the complete evidentiary record. Counsel had initially taken steps to obtain the report, accepted personal responsibility and acted after discovering the omission. Discussions surrounding the pre-trial conference also led counsel reasonably to believe that strict compliance was no longer being insisted upon.
The defendant retained substantial time to respond, and the report did not introduce new treatment recommendations.
Reports Served Before and After the Pre-Trial Conference
The pattern of case-law is beginning to illustrate that the timing of the report in relation to the pre-trial conference can affect the reasonable-explanation and prejudice inquiries.
A report which was served late but sufficiently before the conference will be seen as more likely to allow the parties to:
evaluate the complete expert case;
obtain judicial feedback;
discuss settlement meaningfully; and
address trial-management issues.
If those objectives remain achievable, a documented mistake or unexpected need for responding evidence may be treated more permissively.
A report which served after the pre-trial conference is substantially less likely to be accepted. Although Post-pre-trial service is not always fatal, it seems to make the explanation, the nature of the evidence and the proposed cure especially important.
In Butler v. McConvey, 2025 ONSC 2485, the plaintiffs sought to obtain orthopaedic and future-care-cost reports after the pre-trial conference. The injuries had occurred years earlier, and trial remained approximately eight months away.
The motion was dismissed because the plaintiffs did not reasonably explain why the reports had not been obtained earlier. Future care had been part of the claim from its commencement, and anticipated deterioration did not provide continuing permission to develop a new expert case after the pre-trial conference.
The absence of immediate trial prejudice did not eliminate the requirement for a reasonable explanation.
Why the Default Must Be Addressed Promptly
Once non-compliance is discovered or raised, the responsible party should seek written consent, an extension or other directions without delay. In Forsung v. Neadow, 2023 ONSC 5873, three reports were served shortly before the pre-trial conference. The defence objected, but the plaintiffs did not seek relief until the opening of trial several months later.
The Court excluded the reports. It rejected the explanation and emphasized the failure to address the known default before trial.
Delay in seeking relief can create prejudice separate from the original late service. Courts do not want to see parties unable to obtain rebuttal evidence while the admissibility of the report in question remains unresolved.
Leaving the issue until trial could produce the sequence of additional assessments, responding reports and adjournment requests that the March 31, 2022 amendment was intended to reduce.
Banninger: New Counsel Must Explain the Earlier Delay
A change in counsel does not eliminate the need to explain the full period of default. In Banninger v. Fournier, 2026 ONSC 3035, the defence sought to compel a neuropsychological assessment and serve the resulting report after the Rule 53.03 deadline.
Current counsel acted promptly in arranging the assessment after assuming carriage of the matter. The evidentiary problem was the preceding period of almost two years, during which no assessment had been arranged. There was no evidence from former counsel explaining the delay.
The motion was dismissed. Evidence that new counsel acted diligently did not account for the default as a whole. The proximity of trial and the likely need for an adjournment also weighed against relief.
When Does a Late Expert Report Cause Prejudice or Undue Delay?
The cost of obtaining a responding report is not non-compensable prejudice. Nor is the need to answer an opinion addressing an issue that has remained live in the pleadings.
The concern becomes more serious where the late report:
introduces a new theory shortly before trial;
requires another medical examination or additional testing;
produces sequential reports that cannot be completed before trial;
changes trial preparation undertaken in reasonable reliance on the existing expert record; or
threatens a lengthy fixed trial date.
The party alleging prejudice should support it with evidence and specifics as opposed to bald statements of having been prejudiced. The record may need to identify the proposed responding expert, whether another assessment is required, the expert’s availability and the time reasonably needed to complete the response.
Reliance prejudice may also be relevant. A party may have decided not to retain an expert, made concessions, conducted examinations, evaluated settlement or prepared for trial on the basis of the expert evidence previously disclosed.
A general assertion that the report could cause delay may carry little weight where trial is distant and no evidence addresses the ability to respond. The position is different where a fixed trial is approaching and the report would require new assessments and several rounds of expert evidence.
The court may also consider the consequences of exclusion. A late report may contain the only available opinion on standard of care, causation, income loss or future care. That consequence can be severe, but it does not replace the requirement for a reasonable explanation.
Extensions Under Rule 53.03(4) and Leave Under Rule 53.08
Rule 53.03(4) permits an expert-report deadline to be extended or abridged:
by the judge or associate judge at the pre-trial conference or a Rule 77 conference;
by the court on motion; or
by written consent, provided the agreed change will not affect the scheduled trial date.
Rule 53.08 is framed in terms of leave from the trial judge to call evidence that does not comply with the Rules. A party seeking relief before trial will ordinarily request an extension or abridgment under Rule 53.03(4).
The relationship between the provisions has received differing emphasis in Superior Court decisions. Some decisions stress the case-management discretion available before trial. Others use the Rule 53.08 requirements when deciding whether to regularize late service under Rule 53.03(4).
Harris confirms that the analysis should account for the function of the report, the sequence of service, compliance with the scheduling requirement, the promptness of the response and the presence or absence of prejudice.
Counsel should therefore prepare the motion record to satisfy the amended Rule 53.08 test even where the formal relief sought is an extension under Rule 53.03(4).
A discussion at the pre-trial conference or a reference to an anticipated expert in a brief does not necessarily extend the deadline. The endorsement, order or written consent should clearly provide the required relief.
Evidence Supporting a Motion to Permit a Late Report
The motion should ideally be supported by evidence from the lawyer or another person with direct knowledge of the default. Submissions in a factum are not a substitute for an affidavit explaining what occurred.
The record should provide a complete chronology, including:
when the need for the expert evidence became apparent;
when the action was set down;
whether the parties established the schedule required by Rule 53.03(2.2);
when the pre-trial conference was fixed;
when the expert was contacted and retained;
when the necessary records and instructions were supplied;
what follow-up occurred;
when the default was discovered; and
what steps were then taken.
If the explanation depends on an expert’s delay or unavailability, evidence from the expert or the expert’s office may be required. Where carriage changed, the record should address the periods under both former and current counsel.
If staff error is relied upon, the affidavit should explain the system, the specific failure and why it was not identified earlier.
The evidence should also identify what the report adds to the case. A future-care-cost report that prices recommendations contained in timely medical reports may create less disruption than a new medical opinion introducing a diagnosis or causation theory for the first time.
The proposed order should address the opponent’s legitimate concerns. Terms may include additional time for a responding report, production of the expert’s file, costs, a focused examination, a revised expert schedule or another direction preserving the trial date.
Conclusion
March 31, 2022 marked a significant change in Ontario’s treatment of late expert evidence. The Rule 53.03 deadlines remained in place, but Ontario Regulation 18/22 changed the consequence of failing to comply. The amended Rule 53.08 shifted the burden to the defaulting party, made a reasonable explanation an express requirement and replaced presumptive admission with judicial discretion.
The Courts decisions since the amendment show that the test is stricter without being mechanical. A short calendaring mistake, which is promptly disclosed while an effective pre-trial remains possible, is more likely to be excused. An unexpected expert development may justify a replacement or responding report. Prolonged inactivity, a decision to postpone expert expense or an unexplained period under former counsel are more likely to result in exclusion.
Foster Injury Law acts in serious personal injury litigation across Ontario, including claims requiring medical, rehabilitation, vocational, economic and future-care expert evidence.
By Lane Foster, Ontario Personal Injury Lawyer
