Shared Custody and Child Support: Understanding Section 9

What counts as shared custody

Under the Federal Child Support Guidelines, shared custody applies when each parent has the child at least 40% of the time. This threshold is critical because it changes how child support is calculated.

Below 40%, the standard table applies: the non-residential parent pays the table amount based on their income. At 40% or above, section 9 kicks in and both parents' incomes matter.

The 40% threshold is typically measured by overnight stays over the course of a year. Approximately 146 overnights out of 365 equals 40%.

How section 9 works

When shared custody applies, the court considers three factors:

1. The table amounts for each parent: Look up each parent's table amount as if they were the sole payor
2. The increased costs of shared custody: Maintaining two homes where the child lives increases total costs
3. The conditions, means, needs, and other circumstances of each parent and the child

In practice, the most common approach is the set-off method:

1. Calculate Parent A's table amount (based on Parent A's income and the number of children)
2. Calculate Parent B's table amount (based on Parent B's income and the number of children)
3. The parent with the higher table amount pays the difference

The 40% threshold in practice

The 40% threshold creates a significant cliff in child support calculations. A parent with 39% parenting time pays the full table amount. A parent with 40% triggers the set-off formula, which typically results in a lower payment.

This cliff effect has been criticized, and courts sometimes exercise discretion in borderline cases. However, the 40% line remains the statutory threshold.

What counts toward the 40%?

• Overnight stays are the primary measure
• Daytime-only care may count in some circumstances, but overnights are the standard benchmark
• School time is generally attributed to the residential parent, not the parent who drops the child off at school
• Vacation time counts toward the annual total

Courts look at the actual parenting pattern, not just what the agreement says. If the agreement says 50/50 but the actual practice is closer to 60/40, the court may use the actual pattern.

Section 7 expenses in shared custody

Section 7 special expenses (child care, medical, education, extracurricular activities) are shared proportionally to income regardless of the custody arrangement. Shared custody does not change the section 7 calculation.

If Parent A earns $100,000 and Parent B earns $60,000, Parent A pays 62.5% of section 7 expenses and Parent B pays 37.5%, whether the custody arrangement is sole, shared, or split.

Quebec's approach

Quebec does not use section 9 of the Federal Guidelines. Quebec's Basic Parental Contribution (BPC) model has its own shared custody calculation that differs from the federal approach.

In Quebec's model, shared custody already accounts for both parents' incomes in the base calculation (since the BPC uses combined income). The adjustment for shared custody involves reducing the BPC based on the time each parent spends with the child, rather than using the federal set-off method.

If you live in Quebec, the child support calculation for shared custody is handled differently. Our calculator applies the correct model based on your province of residence.

Common scenarios

Equal incomes, 50/50 custody: When both parents earn the same income, the set-off produces zero child support (since both table amounts are identical). This is the only scenario where shared custody results in no child support.

Unequal incomes, 50/50 custody: The higher earner pays the difference between the two table amounts. With incomes of $100,000 and $60,000 and two children in Ontario, the set-off results in approximately $462/month (compared to $1,245/month under the standard table).

60/40 split: A 60/40 arrangement uses the same set-off formula as 50/50. Both parents' table amounts are calculated and netted. However, courts may adjust the amount based on the specific circumstances, including the actual time split and disproportionate costs borne by the parent with more parenting time.

What courts consider beyond the formula

Section 9 gives courts discretion beyond the simple set-off. Factors that can lead to an adjustment include:

• Disproportionate costs: If one parent bears significantly more of the child-related expenses (such as clothing, school supplies, or activities)
• Standard of living gap: If the set-off would leave the children with a noticeably different standard of living in each household
• Additional children: If one parent has children from another relationship that affect their financial capacity

The set-off is the starting point, not the final answer. Courts can and do adjust the amount when the circumstances warrant it.