When a separating couple has children, two support obligations arise: child support (based on the federal tables) and spousal support (based on the Spousal Support Advisory Guidelines, or SSAG). Many people see the combined monthly figure for the first time and assume it must be wrong — how can they owe $1,500 or $2,000 per month? The combined number can look shocking because most free calculators show a raw total with no explanation of how the two interact or what the after-tax cost actually is.

This article explains the two SSAG formulas — "with child" and "without child" — how child support is always calculated first, what the low/mid/high range means, and why the gross combined figure overstates the real cost to the payor.

Child Support Comes First

The sequencing matters. Child support is calculated first, using the payor's guideline income and the federal child support tables. This amount is fixed by the tables and is not negotiable (absent undue hardship or high-income discretion). Only after child support is determined does the SSAG formula run to calculate spousal support.

The SSAG formula operates on what each household has left after taxes, government benefits, and child support obligations are accounted for. This is why spousal support cannot be calculated in isolation — it depends on the child support amount, which in turn depends on income, province, number of children, and custody arrangement. The two calculations are interdependent.

The Without-Child Formula

When there are no dependent children, the SSAG uses a simpler formula based on gross income. The amount is calculated as a percentage of the difference between the two spouses' gross incomes, scaled by the length of the relationship:

For example, if the payor earns $120,000 and the recipient earns $40,000 after a 10-year marriage with no children, the income difference is $80,000. The low end would be $80,000 × 1.5% × 10 = $12,000 per year ($1,000/month), and the high end would be $80,000 × 2.0% × 10 = $16,000 per year ($1,333/month). Duration would range from 5 to 10 years.

The With-Child Formula

When there are dependent children, the SSAG uses a fundamentally different approach. Instead of a percentage of gross income, the with-child formula targets a specific share of Individual Net Disposable Income (INDI) for the recipient. INDI measures what each parent actually has after taxes, government benefits, and their child support obligations are accounted for.

The target percentages for the recipient's share of combined INDI are:

The formula works by iteratively adjusting the spousal support amount until the recipient's share of combined INDI hits the target percentage. At each step, the full tax calculation is re-run for both parents — because spousal support is tax-deductible for the payor (reducing their taxes) and taxable for the recipient (increasing theirs). Government benefits like the Canada Child Benefit and GST/HST credit are also recalculated, since they depend on adjusted family net income. This is why the calculation requires software — the circular dependency between support, taxes, and benefits cannot be solved by hand.

Worked Example — Combined CS + SS

Consider two parents in Ontario: the payor earns $100,000 and the recipient earns $40,000. They have two children in a shared custody arrangement (50/50) and were together for 12 years.

Step 1: Child Support

Using the current federal tables (SOR/2025-166), the payor's notional table amount for 2 children at $100,000 is $1,517 per month. The recipient's notional table amount at $40,000 is $609 per month. In shared custody, the set-off applies: $1,517 − $609 = $908 per month in child support from the payor to the recipient.

Step 2: Spousal Support (SSAG With-Child)

With child support established, the SSAG formula calculates each parent's INDI — income after taxes, benefits, and child support obligations. At a $100,000 / $40,000 income gap with two children, the recipient's share of combined INDI before spousal support is typically around 38%, below the 40% floor. The formula then iterates to find the spousal support amount that brings the recipient to each target:

The spousal support figures are approximate — the exact amounts depend on the full tax calculation, which accounts for bracket crossovers, CPP/EI, provincial surtaxes, and government benefit clawbacks. The calculator runs this computation iteratively to converge on the precise amount for each scenario.

Step 3: The After-Tax Picture

The combined figure of $1,358 per month at the mid scenario is the gross obligation. But this overstates the real cost to the payor, because spousal support is tax-deductible. At the payor's marginal rate (approximately 43% combined federal and Ontario provincial at $100,000), the tax savings on $450 per month of spousal support is roughly $194 per month. The after-tax cost of the combined obligation is closer to $1,164 per month, not $1,358.

For the recipient, the $908 in child support is received tax-free. The $450 in spousal support is taxable, but at the recipient's lower marginal rate (approximately 25% at $40,000 plus $5,400 in spousal support), the tax on it is roughly $113 per month — leaving a net benefit of about $337 per month from the spousal support component. The recipient's total monthly support income, after tax, is approximately $1,245.

Duration of Spousal Support

Duration rules differ between the two formulas. Under the without-child formula, duration is tied to the length of the relationship: 0.5 to 1.0 years of support per year of cohabitation. Support becomes indefinite (duration not specified) after 20 or more years of cohabitation, or when the recipient's age plus years of cohabitation equals 65 or more and the relationship lasted at least 5 years — the "rule of 65."

Under the with-child formula, duration is anchored to children's milestones rather than marriage length alone. The minimum duration runs until the youngest child starts full-time school. The maximum duration runs until the youngest child finishes high school. For parents with young children, this means spousal support can last well beyond what the marriage length alone would suggest — even a short relationship produces a longer minimum duration if the children are very young.

Why the Combined Number Looks Shocking

The "sticker shock" from combined CS+SS is one of the most common reactions in family law. There are three reasons the gross combined figure is misleading: