Services · Damages and Expert Reports
Damages quantification and expert reports
Putting a supportable number on financial loss, and explaining it clearly to counsel, an insurer, or the court. Amir Rosenthal, CPA, CA, LPA, CBV, CFF, works on these files from midtown Toronto for clients across Ontario.
What damages quantification is
When a business says it lost money because of someone else’s actions, a lawyer decides what kinds of loss the law allows it to claim. An accountant then works out how much. The usual question is: what would the business’s results have been “but for” the event, and how do they compare with what actually happened?
The “but-for” comparison (illustration only)
Typical claims
- Breach of contract, including a terminated supply, distribution, or licence agreement.
- Business interruption and other commercial insurance claims, measured under the policy wording.
- Lost profits arising from a shareholder or partnership dispute.
- Misappropriated or unaccounted-for funds, where the amount has to be traced and proven.
What goes into a loss calculation
- The but-for scenario: built from the business’s own history, budgets, contracts, and the market it operates in.
- Actual results: what really happened over the loss period.
- Costs saved: expenses the business did not have to pay because of the event are taken off.
- Mitigation: what the business did, or reasonably could have done, to reduce the loss.
- Timing: how far into the future the loss runs, and how future amounts are stated in today’s dollars.
Expert reports in Ontario
In a civil action in the Superior Court of Justice, an expert who will give opinion evidence has to serve a written report. Rule 53.03 of the Rules of Civil Procedure sets out what it must contain, including the expert’s qualifications, the instructions received, the opinion and reasons, the factual assumptions, the documents relied on, and a signed Form 53 acknowledgment of the expert’s duty. Amendments in force since September 1, 2026 also require the expert to certify that quotations in the report accurately reproduce their sources.
Rule 4.1.01 sets out that duty: an expert must give opinion evidence that is fair, objective, and non-partisan, limited to matters within their expertise. That duty to the court comes ahead of any obligation to the party paying for the report. Family court and tribunals have their own rules; counsel will confirm which apply.
How an expert engagement usually runs
- RetainerCounsel sets out the question, the parties, and the timetable. Conflicts are checked.
- DocumentsFinancial records, contracts, pleadings, and any reports already served.
- AnalysisBuild the but-for case, measure actual results, and test key assumptions.
- ReportA written report with the contents Rule 53.03 requires and a signed Form 53.
- Next stepsResponding reports, meetings of experts, mediation, or testimony where needed.
This page is general information, not legal advice. What can be claimed, and the deadlines for serving expert reports, depend on the case and the court; your lawyer will advise.
Related pages: forensic accounting, shareholder disputes, family-law valuation, and business valuation.
Damages and expert report questions
What does “quantifying damages” mean?
It means putting a supportable dollar figure on financial harm. The usual approach compares what actually happened with what would most likely have happened if the event had not occurred (the “but-for” scenario). The difference, adjusted for costs saved and for what the business did or could have done to reduce the loss, is the measure of loss.
What kinds of claims need this work?
Breach of contract, lost profits from a terminated agreement, business interruption and other insurance claims, shareholder and partnership disputes, and claims involving misappropriated funds are common examples. The legal test for what is recoverable comes from the law and the contract; the accountant measures the amount.
What must an expert report include in Ontario?
For civil actions in the Superior Court, Rule 53.03 of the Rules of Civil Procedure lists the contents: the expert’s name, address, area of expertise and qualifications; the instructions received; the nature of the opinion sought; the opinion and reasons; the factual assumptions; any research; a list of the documents relied on; and a signed acknowledgment of the expert’s duty (Form 53). Since September 1, 2026, the expert must also certify that quotations in the report accurately reproduce their sources.
Who does the expert work for?
An expert is retained by a party or by counsel, but under Rule 4.1.01 the expert’s duty is to the court: to give opinion evidence that is fair, objective, and non-partisan, and only on matters within their expertise. That duty comes first.
Can you review the other side’s expert report?
Yes. A critique or responding report reviews the assumptions, data, and calculations in another expert’s report and explains where they affect the result. The same duty of independence applies.
Is this only for court cases?
No. Many loss claims are resolved in negotiation, mediation, or with an insurer. A clear calculation of loss helps in all of those settings, whether or not the matter reaches a courtroom.
Complimentary discussion
If counsel is involved, mention the timetable and any deadlines for expert reports when you call or write.