How Child Support Is Calculated in Ontario

What Determines the Basic Amount?

For most families, the starting point for child support is a "table amount" set out in the applicable Child Support Guidelines. The table amount is generally driven by three inputs: the paying parent's annual income (sometimes called "guideline income"), the number of children being supported, and the province or territory where the paying parent lives. Feed those three inputs into the applicable table, and it produces a base monthly amount.

This page is a deep dive into how that number is actually arrived at — the guidelines that apply, how income is defined and sometimes adjusted, and how the table amount relates to other parts of a support calculation. For a broader overview of child support in Ontario generally, including enforcement and how support interacts with separation agreements, see Child Support in Ontario: A Complete Guide.

It helps to think of the calculation as a sequence rather than a single step. First, a parent's guideline income has to be determined — which, as described below, is not always as simple as reading one line off a tax return. Second, that income figure is matched against the applicable table for the relevant number of children and province of residence. Third, the result is checked against the parents' actual parenting-time split, since shared or split arrangements can change how the table amount is applied. Only after those steps are complete does it make sense to layer on any special or extraordinary expenses. Skipping ahead to a table lookup before guideline income and parenting time are properly sorted out is one of the most common sources of disagreement between parents.

The Federal vs. Ontario Guidelines

Child support calculations in Canada are generally governed by one of two closely related sets of rules. The Federal Child Support Guidelines are a regulation made under the federal Divorce Act, and they apply when spouses are married and pursuing a divorce. The tables attached to the Federal Guidelines are what most people picture when they think of "the child support tables."

Ontario also has its own Child Support Guidelines, a regulation made under the provincial Family Law Act. These apply to parents who are not going through a divorce — because they were never married, or are married but not seeking a divorce. Ontario's Guidelines are closely modelled on the federal version, so the calculation concepts described on this page — the table amount, guideline income, imputed income, and special expenses — work essentially the same way under either set of rules. Which set technically governs your case can still matter procedurally, so if you are unsure, confirm which applies before relying on either.

What Counts as "Income" for Support Purposes

A common misconception is that "income" for child support purposes is simply whatever appears on a pay stub or a single line of a tax return. In many straightforward cases, the starting point genuinely is close to that — commonly the total income reported on a recent tax return — because the Guidelines tables are themselves built around gross (before-tax) income and already reflect typical tax effects.

But guideline income is not always identical to a tax return figure. The Guidelines allow certain amounts to be added to or subtracted from a parent's reported income in defined circumstances, and income from sources like self-employment, dividends, or non-arm's-length arrangements can require a closer look before a final guideline income figure is reached. In other words, "income" for child support purposes is a defined concept under the Guidelines, not always a single number you can read directly off a tax slip.

Income can also fluctuate year to year — from bonuses, overtime, seasonal work, or a job change — and parents do not always agree on which year, or which averaging approach, best reflects a fair ongoing figure. Many separation agreements and court orders address this by requiring parents to exchange updated income information annually, so the guideline income figure can be revisited as circumstances change rather than left to become stale.

When Income Is Imputed or Adjusted

Courts have the ability to "impute" income — meaning they assign a parent an income amount that differs from what that parent actually reports — where reported income does not fairly reflect a parent's ability to pay support. This is generally an exception rather than the default, and it applies in specific, recognized circumstances rather than at large. Examples commonly raised in these cases include a parent who appears to be intentionally underemployed or unemployed without a reasonable explanation, a parent whose income appears to have been diverted, or a parent who unreasonably deducts expenses that reduce their reported income.

Whether income should be imputed, and by how much, is a fact-specific determination made case by case — courts weigh evidence about a parent's work history, qualifications, and circumstances rather than applying a fixed formula. This is one of the more commonly disputed parts of a support calculation, which is part of why professional guidance is often valuable when income is not straightforward.

Table Amount vs. Special Expenses

It helps to keep two separate pieces of a support calculation distinct. The table amount is meant to cover the ordinary, day-to-day costs of raising a child and is calculated from income, the number of children, and province of residence alone. Special or extraordinary expenses — sometimes referred to by practitioners as "section 7" expenses — are additional costs layered on top of the table amount, such as childcare, uninsured health-related costs, or certain education or extracurricular expenses. These are generally identified separately and shared between parents roughly in proportion to their respective incomes, rather than being built into the table amount itself.

For a detailed look at what qualifies as a special expense and how sharing is generally worked out, see Special and Extraordinary Expenses.

Shared Parenting and the Calculation

The standard table-lookup approach assumes one parent has the child most of the time. When parenting time is shared close to equally between both parents, the calculation is generally adjusted rather than simply set aside. Courts and the Guidelines recognize that shared parenting arrangements can involve additional costs, since both households need to be equipped to care for the child, and the calculation in these situations commonly looks at factors beyond a simple table lookup for one parent.

Because this is one of the more nuanced areas of a child support calculation, it is covered in its own dedicated guide: see Shared Parenting and Child Support for a fuller explanation of how these arrangements are generally approached.

Self-Employment and Complex Income

Calculating guideline income is generally more involved when a parent is self-employed, earns significant income from a corporation they control, or has income from multiple or irregular sources. Business revenue is not the same thing as personal income available for support purposes, and certain business deductions that are legitimate for tax purposes may not be treated the same way when guideline income is being determined. Depending on how complex the income picture is, arriving at a guideline income figure can range from a fairly simple exercise to one that requires financial statements, professional accounting input, or a more detailed court process.

If your own or the other parent's income involves self-employment, investment income, or a similarly complex picture, this is generally an area where professional input is most valuable, since general guidance cannot substitute for a review of the actual numbers involved.

This is also where the idea of a "simplified" calculation versus a more complex one tends to come up in practice. Where a parent's income is a single, stable salary with a clear tax slip, arriving at a guideline income figure and looking up the table amount can be quick and largely mechanical. Where income is mixed, irregular, or tied up in a business a parent controls, reaching a defensible guideline income figure can instead involve financial statements, prior years' returns, and sometimes expert input — meaning the same basic table-lookup framework applies, but getting to the right income figure takes considerably more work.

Where to Get an Actual Estimate

This page deliberately avoids stating specific table amounts, since the government tables are updated periodically and a number printed here could quickly become outdated or simply wrong for your situation. For a general, unofficial starting estimate once you understand the mechanics described above, this site plans to publish an informational child support calculator — intended purely as a general educational estimate, not a substitute for the official government look-up tool or for professional advice tailored to your income and circumstances.

Common Mistakes

• Assuming take-home pay, rather than gross guideline income, is the relevant figure
• Treating self-employment or business income the same as employment income without a closer look
• Overlooking that special expenses are shared separately from the table amount
• Assuming close-to-equal parenting time automatically eliminates support
• Relying on an outdated table amount or an unofficial estimate as if it were final
• Not revisiting the calculation after a meaningful, ongoing change in either parent's income
• Assuming a court will accept a lower reported income without questioning whether it fairly reflects earning capacity
• Trying to resolve a complex, self-employment income dispute without any professional input

Frequently Asked Questions