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By Rebecca Winninger, Senior Associate Research Lawyer, Lam Family Law*

It can be tricky to explain to clients how an appeal differs from a trial, and to unpack the concept of “deference to the trial judge”. But this is a key conversation to have when considering an appeal, so the client can weigh their options and chances of success. The standard of review has been described as “the starting point in any appeal”: Cronier v. Cusack, 2023 ONCA 178 (CanLII), at para 8.

Below, we set out the general standards of review for questions of law, fact, and mixed fact and law, and then provide some subject-specific references for family law appeals.

How exactly you phrase the standard of review may change depending on whether you act for the appellant or the respondent. Rather than using the same boilerplate language for every appeal, it can be worthwhile to do some brief research on the applicable standard to see if you can characterize the issue as one that attracts more or less deference. Ultimately, however, it’s important to be honest about what the standard is – the ONCA has frowned on efforts to “distort” the standard of review: Karatzoglou v. Commisso, 2023 ONCA 295 (CanLII), at para 14. Your summary of the applicable standard should also be concise. I once attended a CPD program where an ONCA judge said that he did not want “paragraphs and paragraphs” on the standard of review.

The Appellate Standard of Review

Errors are generally divided into three categories: questions of law, questions of fact, and questions of mixed fact and law.

In simple terms, “questions of law are questions about what the correct legal test is; questions of fact are questions about what actually took place between the parties; and questions of mixed law and fact are questions about whether the facts satisfy the legal tests”: Rosenberg v. Yanofsky, 2019 ONSC 6886 (CanLII), at para 17.

The three categories attract different standards of review. On a pure question of law, the standard of review is correctness, and the appeal court can “replace the opinion of the trial judge with its own”: Housen v. Nikolaisen, 2002 SCC 33 (CanLII), at para 8.

The standard of review for findings of fact is that they cannot be reversed unless the hearing judge made a “palpable and overriding error”: Housen v. Nikolaisen, ibid, at para 10. A “palpable” error is one that is obvious. Overriding “means capable of changing the result of the case.” Justice Stratus recently observed that “these two things very seldom happen together” and “reversal on this ground is rare indeed”: Patel v. Dermaspark Products Inc., 2025 FCA 145 (CanLII), at para 9. The same stringent standard applies to inferences of fact: Housen v. Nikolaisen, 2002 SCC 33 (CanLII), at para 23.

Errors of mixed fact and law fall along a spectrum. Where the error arises from “an incorrect standard, a failure to consider a required element of a legal test, or similar error in principle, such an error can be characterized as an error of law, subject to a standard of correctness.” However, “[w]here the legal principle is not readily extricable, then the matter is one of “mixed law and fact” and is subject to a more stringent standard”: Housen v. Nikolaisen, ibid, at para 36. An extricable question of law is one where a legal question “predominate[s] or fundamentally taint[s] the question of mixed fact and law.”: Patel v. Dermaspark Products Inc., 2025 FCA 145 (CanLII), at para 7.

The Standard of Review in Family Law Appeals

Property Cases
Orders resolving financial disputes in family law cases are entitled to significant deference: Lesko v. Lesko, 2021 ONCA 369 (CanLII), at para 5. The standard of review is designed to promote finality in family law litigation and to recognize the importance of the appreciation of the facts by the trial judge. Minor calculation errors will not meet this stringent standard of review: Stetco v. Stetco, 2014 ONCA 370 (CanLII), at para 6.

Determining the date of separation is a question of fact and is entitled to deference: Tsarynny v. Topchiy, 2025 ONCA 175 (CanLII), at para 18.

The value of an asset is a question of fact: Ackerman v Ackerman, 2014 SKCA 137 (CanLII), at para 25, and so is the amount of an outstanding liability: Houston v. Houston, 2011 ONSC 5610 (CanLII), at para 21.

However, the interpretation of the Family Law Act with regard to the inclusion of a liability in Net Family Property has been held to be a question of law attracting the standard of correctness: Houston v. Houston, ibid, at paras 3-8. In general, statutory interpretation is a question of law: 2544176 Ontario Inc. v. 2394762 Ontario Inc., 2022 ONCA 529 (CanLII), at para 18.

In decisions regarding unequal division of net family property under s. 5(6) of the Family Law Act, the court must be correct on the law, and the factual findings must not raise a palpable and overriding error. In the exercise of discretion to award or decline to award an unequal division, appellate “intervention is warranted only if there is a misdirection or decision so clearly wrong that it amounts to an injustice”: Ward v. Ward, 2012 ONCA 462 (CanLII), at para 21, citing various cases.

Decisions in unjust enrichment and remedial constructive trust claims are very fact-specific, and the applicable standard of review is generally that of palpable and overriding error: Iredale v. Dougall, 2025 ONCA 266 (CanLII), at para 17. The existence of a joint family venture is a question of fact: Martin v. Sansome, 2014 ONCA 14 (CanLII), at para 51.

In a resulting trust claim, the actual intention of the transferor is a question of fact: Andrade v. Andrade, 2016 ONCA 368 (CanLII), at para 107.

A “high standard of review applies to a trial judge’s discretionary prejudgment interest award. Absent reversible error, there is no basis to interfere with a trial judge’s discretionary decision” on this issue: R.L. v. M.F., 2025 ONCA 595 (CanLII), at para 22.

Spousal Support
The standard of review for support decisions is one of significant deference. An appeal court should only intervene where there is a material error, a serious misapprehension of the evidence, or an error of law. It is not entitled to overturn a support order “simply because it would have made a different decision or balanced the factors differently”: Cheng v. Sze, 2021 ONCA 346 (CanLII), at para 3, citing Hickey v. Hickey, 1999 CanLII 691 (SCC), at para 12.

“This approach promotes finality in family law litigation and recognizes the importance of the appreciation of the facts by the trial judge”: Plese v. Herjavec, 2020 ONCA 810 (CanLII), at para 34; Ballanger v. Ballanger, 2020 ONCA 626 (CanLII), at para 22. See also R.L. v. M.F., 2025 ONCA 595 (CanLII), at para 21.

The deferential standard “applies with particular force in family law cases where the trial judge’s findings of fact are rooted in credibility assessments”: Cheng v. Sze, 2021 ONCA 346 (CanLII), at para 3, citing Jonas v. Pacitto, 2020 ONCA 727 (CanLII), at para 42.

Deference is also “augmented for payor incomes over $350,000”: R.L. v. M.F., 2025 ONCA 595 (CanLII), at para 20.

A hearing judge’s determination of entitlement to share in a payor’s post-separation income increases gives rise to significant deference on appeal: R.L. v. M.F., ibid, at para 20.

Child Support
“[C]hild support orders attract deference on appeal. The hearing judge’s findings and inferences of fact may not be disturbed on appeal absent an error on an extricable question of law, a palpable and overriding error, or a fundamental mischaracterization or misapprehension of the evidence”: Douglas v. Faucher, 2025 ONCA 293 (CanLII), at para 22, citing Michel v. Graydon, 2020 SCC 24, at para 30.

The calculation of child support arrears is a question of fact: Burns v. Brown, 2021 ONCA 450 (CanLII), at para 24.

Whether a child is still a “child of the marriage” under the Divorce Act is a finding of mixed fact and law that is entitled to deference: Slongo v. Slongo, 2017 ONCA 272 (CanLII), at para 23.

A hearing judge errs in law if they fail to consider whether a s. 7 expense is both necessary and reasonable: A.E v. A.E., 2021 ONSC 8189 (CanLII), at para 379.

Parenting
The determination of parenting orders involves issues of mixed fact and law: A.C.V.P. v. A.M.P., 2022 ONCA 283 (CanLII), at para 18.

Parenting decisions “are inherently an exercise of discretion…As a result, an appellate court must act with restraint and may only intervene where there has been ‘a material error, a serious misapprehension of the evidence, or an error in law’ [citations omitted]. An omission is only a material error ‘if it gives rise to the reasoned belief that the trial judge must have forgotten, ignored or misconceived the evidence in a way that affected his conclusion’”: B.J.T. v. J.D., 2022 SCC 24 (CanLII), at para 56.

An appellate court cannot “redo a lower court’s analysis to achieve a result that it believes is preferable in the best interests of the child”: B.J.T. v. J.D., ibid, at para 57.

However, it is an error of law for the court to mischaracterize the parenting issue at trial: Berry v. Berry, 2011 ONCA 705 (CanLII), at paras 23 & 25. It is also an error of law to place the burden of proof on the wrong party: Sferruzzi v. Allan, 2013 ONCA 496 (CanLII), at para 45.

*with thanks to Maria Golarz for her suggestions and edits.