Child Support Right After Separation in Ontario: When Does It Start?

If the children are living with you after separation, you may be facing rent, food and childcare costs with less income than before. The natural question is whether support begins on the day you separate or only once something is signed or ordered.

This article explains how child support is set, how a claim for earlier months works, and how interim support can bridge the gap. It is general information, not legal advice, and a lawyer can apply it to your facts.

How child support is set

Ontario child support is based on the number of children, the province where the payor lives and the payor's annual income. New federal child support tables apply to all Ontario child support matters starting October 1, 2025. Because tables change, check current amounts rather than relying on older figures you may have heard.

There are three main routes to a support arrangement: the online Child Support Service, where both parents enter information, a written agreement, or filing in court. The online tool is not available to people who earn more than $150,000 or less than $12,000 annually, or where the recalculated amount includes post-secondary education expenses.

When does support actually start?

Support is arranged by agreement, online through the Child Support Service, or by court order. Whether and how far back a claim can reach depends on when the issue was raised. If you wait, you may be able to claim for earlier months, but that is not guaranteed, and it depends on the facts.

The key idea is effective notice. Under the Supreme Court of Canada's approach as summarized by Justice Canada, retroactive child support generally runs from the date of effective notice, and raising the issue does not need to involve legal action. In other words, a clear written request to the other parent can matter. It is also usually inappropriate to go back more than three years before formal notice.

The Court of Appeal for Ontario has reaffirmed both the effective-notice starting point and the three-year presumption. A payor who does not disclose a material increase in income may be treated as having engaged in blameworthy conduct, which can move the date back.

Getting support while the case is ongoing

A court can order child support, including interim orders, and the order must follow the applicable guidelines. An interim order is meant to provide support until the case is resolved.

In Ontario, a family case starts with Form 8 (General Application) where the parties disagree. Motions use Form 14 (Notice of Motion) and Form 14A (Affidavit). You will also need a financial statement, which is Form 13 where only support is claimed or Form 13.1 where property or debts are claimed.

Proof of income and later changes

The payor must give proof of income, meaning a tax return and notice of assessment, every year, within 30 days of the original order or agreement date unless agreed otherwise. That is why tax records matter even when everyone is on good terms.

If circumstances change later, a final order is changed by Form 15 (Motion to Change), or Form 15C if the parties consent. Form 15D is used for child support only, by consent. Child support is also enforceable; the Family Responsibility Office enforces support and can take money from bank accounts, suspend a driver's licence or start a court case.

What to do next

• Put your request for support in writing and keep a dated copy; this may help show effective notice.
• Gather your recent tax returns and notices of assessment, and the other parent's if you have them.
• Record when the children live with each parent and the major expenses you are covering.
• Decide whether an online application, an agreement or a court application suits your situation.
• If money is urgent, ask a lawyer about an interim order.
• Speak with a Family Law Information Centre for free information, understanding that staff do not give legal advice.

If you are unsure what to call your living arrangement, or whether parenting time affects the amount, a lawyer can explain how your facts apply.

Frequently asked questions