Contino v Leonelli-Contino: The 40% Rule for Child Support in Ontario

The 2005 Supreme Court of Canada decision in Contino v. Leonelli-Contino is the case every Ontario parent with shared custody needs to understand. It sets the framework for how child support is calculated when both parents exercise at least 40% of parenting time — and it's more nuanced than most parents realize.

The 40% Threshold

Under Section 9 of the Federal Child Support Guidelines, shared custody exists when each parent has the child for at least 40% of the time over the course of a year. That translates to:

• 146 overnights out of 365
• 3,504 hours of physical responsibility out of 8,760

Below 40%, the standard table amount applies — calculated using only the payor parent's income, with no consideration of the recipient's earnings. Above 40%, the court applies the Contino framework, which considers both parents' incomes and the actual costs of the shared arrangement.

The financial difference at this threshold can be significant — often hundreds of dollars per month in adjusted support.

The Contino Three-Part Test

The Supreme Court rejected a simple "set-off and done" approach to shared custody support. Instead, Contino requires courts to consider three factors:

1. The Set-Off Amount

Calculate what each parent would pay the other under the standard table. The basic set-off is the difference between these two amounts. If Parent A's table obligation is $1,200/month and Parent B's table obligation is $500/month, the starting set-off is $700/month from Parent A to Parent B.

2. Increased Costs of Shared Custody

Shared custody is more expensive than a primary-residence arrangement because both parents maintain full-time household setups for the child: two bedrooms, two sets of clothing and supplies, duplicate school equipment. The court adjusts the set-off amount to account for these increased costs, which typically fall disproportionately on the lower-income parent.

3. Conditions, Means, Needs, and Standard of Living

The court examines whether the set-off amount (as adjusted for increased costs) actually reflects the child's standard of living in each home. If there's a significant income disparity, the court may adjust support to ensure the child doesn't experience drastically different living conditions between households.

What Contino Means in Practice

The three-part test means that shared custody support isn't a simple formula. Two families with identical incomes and identical 50/50 schedules can end up with different support amounts depending on their specific costs, housing situations, and the child's needs.

This is why "just get to 40% and pay less" is a risky strategy. Courts look unfavorably at parents who engineer their schedule primarily to reduce support obligations. If a judge concludes that the motivation behind a shared schedule is financial rather than child-focused, they may give less weight to the parenting time percentage and more weight to the child's actual needs.

Common Mistakes

Assuming the set-off is the final number. The set-off is step one of three. Courts regularly adjust the amount upward or downward based on the other factors.

Ignoring the income disparity. If one parent earns $150,000 and the other earns $40,000, a straight set-off may leave the lower-income parent unable to maintain a reasonable standard of living for the child during their parenting time. Courts account for this.

Failing to document actual parenting time. If you claim 50% but routinely cancel or shorten your parenting time, the court may recalculate based on actual overnights rather than the scheduled arrangement.

Confusing parenting time with decision-making. The 40% threshold is about physical time with the child, not about who makes decisions. You can have sole decision-making responsibility and still be in a shared custody support arrangement if both parents meet the 40% threshold.

Getting It Right

If your parenting time is near the 40% line, precision matters. Track every overnight, account for holiday and summer schedule adjustments, and calculate your annual percentage before negotiating support.

The Ontario Child Custody & Parenting Plan Guide includes a parenting time tracking worksheet and a Section 9 shared custody calculation walkthrough based on the Contino framework — so you can model different schedule scenarios and understand their financial implications before mediation.

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