Section 3 child support is the base amount that is paid each month. It is based on the payor's Guideline Income, number of children, and payor's province (to account for differences in provincial tax rates).

Section 3 child support is expected to contribute towards regular expenses such as food, shelter, clothing, transportation, usually public school registration fees and supplies, and sometimes some low cost extracurricular activities such as the rec centre.

In Shared Parenting (for child support purposes, where each parent has at least 40% of parenting time), section 3 child support is generally treated as if each parent pays the other the calculated "Table amount", so that only a "net" or "set-off" amount is payable. However, courts do not necessarily have to follow the set-off amount, depending on the factors set out in a Supreme Court of Canada decision referred to as Contino (Contino v. Leonelli-Contino, 2005 SCC 63), which considers:

1. The amounts set out in the applicable tables for each of the spouses (the amount calculated based on their Guideline Income, province, and number of children);
2. The increased costs of shared custody arrangements (for example, if one parent still pays the majority of expenses, such as where split evenings means that one parent still takes care of transportation to and from school/activities and meals); and
3. The conditions, means, needs and other circumstances of each spouse and of any child for whom support is sought (we can look at income that usually wouldn't be included in calcualtions, such as certain tax benefits, as well as assets and debts).

In split parenting (see "Other Forms Of Parenting Time"), each parent pays section 3 child support based on the number of children residing in the other parent's household. After each parent's child support obligation is calculated, again only a "net" or "set-off" amount is payable, although the Contino factors do not apply to split parenting.

The Government of Canada's child support Table Look-up can be found at: https://www.justice.gc.ca/eng/fl-df/child-enfant/cst-orpe.html

Courts need not stick to the calculation where income is over $150,000. That's because at some point, child support will go beyond a child's reasonable needs, it is not meant to be spousal support. However in practice it is very rare to see any difference to child support until income is over $300,000 or even higher, and there are decisions where a parent made nearly a million dollars a year and child support was not reduced. Child Expense Budgets would often be exchanged. There would need to be "clear and compelling evidence" that departing from the ordinary calculation is appropriate. This could arise where parents were very frugal during the relationship, or a one-time payment resulted in a high income that parents likely wouldn't have spent during the relationship, for example selling a rental property or an injury settlement meant to compensate for future lost income over many years.

In very rare circumstances, courts might reduce support payable, known as an Undue Hardship application.

More principles are contained in the Child support basics page.