How does shared (50/50) custody change child support in Ontario?

You usually still pay — just less. When each parent has the children at least 40% of the time, Ontario does not cancel child support. It switches to the section 9 set-off: each parent's table amount is worked out, and the higher earner pays the difference. Equal time changes who pays. It does not zero the cheque.

This catches a lot of separated fathers off guard. The assumption is that 50/50 parenting means no support. The Federal Child Support Guidelines, the federal rules Ontario uses, treat it differently once you cross the 40% line. Section 9 replaces the straight table amount with a calculation that uses both incomes — a step beyond how child support is normally calculated.

When this does apply

Section 9 applies when each parent has the children at least 40% of the time over the year, roughly 146 overnights or more. At that point child support is worked out in three steps:

1. Calculate the table amount each parent would pay on their own income, the monthly figure from the Federal Child Support Tables.
2. Set off the two amounts so the higher earner pays the difference.
3. The court can adjust the figure up for the added cost of running two homes.

Example with round numbers. You earn $100,000, and your table amount for two children is $1,517. Your co-parent earns $60,000, with a table amount of $911. The set-off is $606 a month, paid by you. The starting point is the difference, not zero. The Department of Justice walks through the same shared-custody step. For the table figures themselves, see the Federal Child Support Tables.

Parent	Income	Table amount (2 kids)
You	$100K	$1,517
Co-parent	$60K	$911
Set-off payable	—	$606

$606/month set-off ($100K vs $60K, 2 children)

When this doesn't apply

Below the 40% line, section 9 does not apply. If your co-parent has the children most of the time and you have them every other weekend, you pay the straight table amount on your income, with no set-off. The threshold is usually counted in overnights across the year, not a loose sense of sharing the load, so a few nights either way can move you across it. Steps to Justice explains how the count works.

Two cautions. Section 9 is not a guaranteed clean subtraction — a judge can order more than the set-off because two homes cost more than one. And if either parent's reported income looks artificially low, the court can impute income before running the math.

What counts as 40%: overnights vs daytime hours

The 40% threshold is usually counted in overnights — the nights a child actually sleeps at your home — and roughly 146 of them across the year puts you at the line. Some courts count hours or a mix — there is no single fixed method. Daytime hours on a day that ends at the other parent's home do not, on their own, push you over it. Where a day is genuinely split and hard to label, Ontario courts decide it case by case, looking at who carries the day-to-day care and cost on that day rather than counting hours on a stopwatch. That is why a clean, dated record of where the children sleep matters most for anyone sitting close to the line.

What to do

Count the overnights before you assume anything. Add up the nights the children spend with you across a full year. If the total reaches 40% or more, calculate both table amounts and the set-off rather than guessing. Run both incomes through the free calculator so you see the real difference, not a rough half. If you sit close to the 40% line, keep a dated record of where the children sleep, because at the threshold a handful of nights changes the number. If a lasting shift in parenting time later carries you across the line, that can be a material change in circumstances and a reason to change a child support order. The set-off still sits on top of the base rules in how child support is calculated.

Run the free calculator at cairnguide.ca/calculator.