Understanding the 40% Threshold in Child Support: What It Means for You

 

When parents separate or divorce, one of the most important questions to answer is: how will we support our children? In Canada (and specifically in Ontario), child support is governed by the Federal Child Support Guidelines, which aim to ensure children benefit from both parents’ financial resources as if they were still living together.

But what happens when parenting time is shared more equally?

That’s where the 40% threshold comes in—a key rule that changes how child support is calculated when both parents share substantial time with their children.

What is the 40% Threshold?

Under the Federal Child Support Guidelines, Section 9, a parent is considered to have shared custody (or “shared parenting”) if they have the child in their physical care at least 40% of the time over the course of a year. That “40%” isn’t about decision-making authority (which is custody in the legal sense) but the actual time spent with the child.

How is 40% calculated?

• Courts often count overnights (e.g., 6 out of 14 nights = ~43%).
• Some courts look at hours in the day to be more precise, especially in disputes.
• School time or daycare time is generally not “neutral”—it’s typically assigned to the parent who has responsibility during those hours.

In other words: you don’t get “credit” for a full day if you only have a child for an evening visit. Courts may use days or hours depending on the facts, but the key is to establish an objective measure to see if the threshold is met.

Why Does the 40% Threshold Matter?

If neither parent meets the 40% threshold, the non-primary parent generally pays the full Child Support Guidelines amount.

BUT

Once both parents have 40% or more of the time, the court can depart from the standard guideline amount. This recognizes that shared parenting usually means duplicated costs (e.g., bedrooms in both homes, clothing, school supplies).

How is Child Support Calculated in Shared Custody?

Once the 40% threshold is met, the court engages in a Section 9 analysis. Here’s what that analysis includes:

 

1. Calculate the “Set-Off” Amount

1. Figure out what each parent would pay under the Guidelines if the other had sole custody.
2. Subtract the lower amount from the higher amount.
3. This difference is the “set-off” amount—often the starting point for support in shared custody.

 

Example: 

1. Parent A would pay $1000/month
2. Parent B would pay $600/month
3. Set-off = $400/month (Parent A pays B)

BUT this is just the starting point—not the final answer.

 

2. Consider the Increased Costs of Shared Custody (Section 9(b))

Shared parenting isn’t always cheaper. Courts examine:

• Are there duplicated expenses? (beds, clothes, toys, food in both homes)
• Have total costs for raising the child gone up overall?

Parents must show actual budgets and financial statements. Courts don’t simply assume shared custody costs more (or less)—they demand evidence.

 

3. Consider the Conditions, Means, Needs, and Circumstances (Section 9(c))

This is the broadest part of the analysis. Courts look at:

• Each parent’s income, assets, debts
• The child’s needs and lifestyle
• The standard of living in both households

A big goal here: avoid major discrepancies in standard of living between homes.

 

4. Exercise Judicial Discretion

Section 9 gives courts flexibility.

• There’s no fixed formula.
• Judges can adjust the set-off if evidence shows it would unfairly burden one parent or harm the child’s standard of living.
• In some cases, the judge might order an amount above or below the Guidelines, or even choose the full Guidelines amount despite shared custody if warranted.

This means outcomes can vary, depending on the facts of each case.

Important Disclaimer: Protecting Children’s Standard of Living

Courts have made it clear (including in Supreme Court of Canada decisions) that a child should not suffer a noticeable decline in their standard of living simply because parenting arrangements have changed. When child support is recalculated after a move to shared parenting, the court’s job is to ensure that the child continues to benefit fairly from both parents’ resources.

This principle is central to every child support determination.

 

Final Thoughts

Shared parenting introduces complexity into child support calculations. Meeting the 40% threshold is only the first step. From there, the law requires a careful, evidence-based analysis of real costs and the circumstances of both families. If you’re trying to understand how the 40% rule might affect you—or negotiating child support in a shared parenting arrangement—it’s wise to get professional legal advice.

At Round Table Legal Services, we help parents:

• Assess if the 40% threshold is met
• Gather and present the right financial evidence
• Negotiate fair and workable child support agreements
• Ensure their child maintains a strong, stable standard of living

 

We know that these discussions can be sensitive and emotional. Our goal is to support you with clarity, compassion, and skill, so you can focus on what matters most: your child’s well-being. If you have questions about shared parenting, child support calculations, or your rights and obligations under the law, reach out to Round Table Legal Services today. Let’s work together to find solutions that protect your child’s future.