Child Support Income in Canada: Line 15000 Explained

The first time a lawyer told me child support "comes off line 15000," I nodded like I understood. I did not. I went home, opened my tax return, found line 15000, and thought: that's it? That number decides everything?

Almost. Line 15000 is where the math starts in Canada, not where it ends. Between that number on your T1 and the number a court actually uses, there's a section of the Federal Child Support Guidelines and a whole schedule of adjustments that can move your income by thousands of dollars in either direction. Here's how child support income determination actually works, in plain English, from a divorced dad in Montreal who had to learn it the slow way.

I'm not a lawyer. I'm a product manager with three kids and a lot of receipts. Everything below points back to the actual regulation so you can check it yourself.

What is Line 15000 and why does child support start there?

Line 15000 is the "total income" line on the T1 General tax return. It's the sum of everything the CRA counts as income before any deductions: employment income, self-employment, investment income, EI, pension, taxable dividends. Child support in Canada starts there because the Guidelines say so, and because a filed return is harder to argue with than a self-reported number.

If you filed taxes before 2019, you knew this line as line 150. The CRA renumbered the return that year and added zeros, so line 150 became line 15000. Same number, new label. Older separation agreements still say "line 150," and that's fine, it means the same thing.

The important part: line 15000 is gross income. It's the number before you subtract RRSP contributions, union dues, childcare deductions, or anything else that lands on your net income line. So the income used for support is usually noticeably higher than the income you feel like you have. The first year after my separation, I remember staring at that figure and thinking about how little of it ever touched my bank account.

Note where line 15000 sits: on your notice of assessment as well as your return. That matters, because the notice of assessment is what CRA actually accepted, not just what you filed.

What does Section 16 of the Federal Child Support Guidelines actually say?

Section 16 of the Federal Child Support Guidelines (SOR/97-175) is one sentence long. It says a spouse's annual income is determined using the sources of income set out under the heading "Total income" in the T1 General form issued by the CRA, and is adjusted in accordance with Schedule III. That's the whole default rule, and it's subject to sections 17 through 20.

Read it twice and you'll notice three things.

One: it says sources of income under the Total income heading, not "line 15000." In practice they're the same for most salaried parents, but the wording matters for someone whose income shows up in an unusual place on the return.

Two: the adjustment to Schedule III isn't optional. It's baked into the definition. A lot of parents (and, honestly, a lot of DIY separation agreements) stop at line 15000 and call it a day. That's an incomplete calculation.

Three: "subject to sections 17 to 20" is doing quiet, heavy lifting. Those sections are the escape hatches, and they're where contested cases actually get fought.

You can read the whole regulation on the Justice Laws website. As of the version current to June 2026, it was last amended October 1, 2025. Justice Canada also publishes a step-by-step guide to determining income that's more readable than the regulation itself.

One thing this article isn't about: what support pays for. Base support and the extras on top of it are two different systems, and mixing them up causes more fights than anything else. I covered that split in child support vs shared expenses in Canada.

Which Schedule III adjustments change your child support income?

Schedule III is a list of 13 adjustments applied to Line 15000 to arrive at Guidelines income. Some subtract (union dues, actual capital losses, carrying charges), some add back (capital cost allowance on real property, payments to non-arm's-length people). Most parents only ever trigger one or two. Self-employed parents and landlords trigger several.

Here are the ones that come up most often in real files:

Item 5 catches people off guard. If you own a corporation and pay yourself non-eligible dividends, your return shows a grossed-up figure roughly 15% higher than the cash you got. Schedule III strips the gross-up out and uses the actual dividends. Your Guidelines income drops. That's one of the rare adjustments that works in the payor's favour.

Item 11 goes the other way and is brutal for landlords. Capital cost allowance is a paper deduction, you never wrote a cheque for it, so the Guidelines add it back. Claim $4,800 of CCA on a duplex and your support income goes up by $4,800 even though your bank balance didn't change. Note the wording: real property only. CCA on a laptop or a van isn't added back under item 11.

And item 3.1 is the subtle one almost nobody notices. For the table amount you deduct spousal support received. For Section 7 expenses you deduct spousal support paid. Two different income figures, from the same tax return, in the same case. If your agreement uses one number for both, someone's math is off.

What does the math look like on a real return?

The cleanest way to see how Line 15000, Section 16, and Schedule III fit together is a worked example. Take a self-employed parent who also owns a small rental duplex and pays himself non-eligible dividends from his corporation. His return says one thing. His Guidelines income says another.

Call him Daniel. Ottawa, two kids, separated in 2024.

Daniel's income for child support is $94,790, not $92,400. The difference is $2,390, which at two children is real money over a year, and it's the kind of gap that a spreadsheet built from line 15000 alone would never show.

Now flip it. If Daniel had claimed a $9,000 capital loss and no gains, item 6 would have changed the picture again. If his corporation had paid a salary to his new partner for work she didn't really do, item 9 would have added that back. The adjustments aren't symmetrical and they aren't intuitive. That's the whole reason Schedule III exists.

Once you have both parents' Guidelines income, the table amount comes from the official federal child support lookup tool, by province and number of children. Quebec runs its own model for provincial matters, which looks at both parents' incomes rather than just the payor's. Different math, same starting point: an income figure built from the tax return.

When can a court ignore Line 15000?

Sections 17 through 19 let a court depart from the tax return when the return doesn't tell the truth about what a parent can actually pay. Section 17 covers income patterns and one-time amounts, section 18 covers corporate income for shareholders, and section 19 lets a court impute income entirely. These are the sections contested cases live in.

Section 17 (pattern of income). If determining income under section 16 wouldn't be the fairest result, the court can look at the last three years and pick an amount that's fair and reasonable given fluctuations or a non-recurring amount. This is the answer for the commissioned salesperson whose income swings between $60,000 and $140,000, and for the parent who cashed out a one-time bonus last year.

Section 18 (shareholder, director or officer). If a parent's income as determined under section 16 doesn't fairly reflect all the money available to them, the court can include all or part of the pre-tax income of their corporation. This is the rule that stops someone from paying themselves $45,000 and leaving $200,000 sitting in the company.

Section 19 (imputing income). The court may impute whatever income it considers appropriate. The listed circumstances include a parent who's intentionally under-employed, one who's exempt from Canadian tax or living in a low-tax country, one who has diverted income, one whose property isn't reasonably used to generate income, one who failed to provide income information when legally required to, and one who unreasonably deducts expenses. Subsection 19(2) adds a line worth remembering: whether a deduction is allowed under the Income Tax Act does not, by itself, make it reasonable for child support.

That last point is the one I'd tattoo on a business card. Tax-deductible and support-deductible are not the same test.

What income documents do you have to disclose?

Section 21 sets the disclosure list for an application: personal tax returns for the three most recent years, every notice of assessment and reassessment for those years, a recent statement of earnings for employees, and financial statements plus corporate details for anyone self-employed or running a business. Section 25 keeps the obligation alive after an order is made.

Section 25 is the one to know if you already have an order. The payor must provide those documents on the other parent's written request, not more than once a year, for any of the three most recent taxation years not already provided, plus current information about the status of any Section 7 expenses in the order.

So: once a year, in writing. Not every time you're curious. Not never.

And under section 19(1)(f), refusing to hand over that information is itself a reason a court can impute income to you. Silence is not a strategy here, it's an invitation for someone else to guess your income upward.

How does any of this connect to the expenses you actually argue about?

Guidelines income does two jobs. It sets the base table amount, and it sets the proportional share each parent pays for Section 7 special or extraordinary expenses: daycare, orthodontics, competitive sports fees. If you earn 62% of the combined parental income, you pay 62% of the summer camp bill, not half. That's why the income number matters twice.

Here's where I stop quoting regulations and tell you what my life actually looks like. My income is higher than my ex's, so from the start she told me to just pay for things myself, since she didn't have spare money. Later she started receiving child benefits and agreed to split, but selectively. Judo for my oldest, $130 a month, she said no, she didn't think it was necessary. Then he got injured at practice and she told me she wouldn't pay for any activities at all. Not swimming, not anything. Her exact line, which I think about more than I'd like: "I'm not paying for your impulsive purchases."

For a long time I just absorbed it. It was easier to buy the school supplies myself than to have the argument about why our kids needed them. I never sat down and calculated a proportional share, because I was too busy avoiding a conversation. That's the trap: the Guidelines give you an objective number, and then two exhausted people ignore it because talking about it costs more than paying.

What changed things wasn't the law. It was logging every expense in one place. Once I started tracking, in the first couple of months, I realized I was paying far more than half of everything. Not because anyone cheated me, but because I'd been quietly eating dozens of small costs I never even recorded. $460 for summer camp. $200 for waterpark tickets. Clothes, school supplies, the constant $20 things. The proportional share concept is meaningless if nobody knows what the total was.

If you're in that spot, the sequence is: settle the income figure first (line 15000, then Schedule III), then log every shared expense as it happens, then apply the percentage. Doing it in the other order is how you end up arguing about a $40 haircut at 11pm. I wrote more about the receipt side of this in what you can actually claim on your 2026 taxes as a co-parent, and about the activities fight specifically in extracurricular costs after divorce.

Frequently Asked Questions

What line on the tax return is used for child support in Canada? Line 15000, total income on the T1 General return. Section 16 of the Federal Child Support Guidelines says annual income starts with the sources listed under Total income, then gets adjusted under Schedule III. Line 15000 was called line 150 before the CRA renumbered the return in 2019.

What is Section 16 of the Federal Child Support Guidelines? Section 16 is the default rule for figuring out a parent's annual income. It says income is determined using the sources of income under the Total income heading on the T1 General form, adjusted in accordance with Schedule III. Sections 17 through 20 let a court depart from that default.

Does the Canada Child Benefit count as income for child support? No. The Canada Child Benefit is not taxable, so it never appears on Line 15000 and it is not part of your Guidelines income. Its predecessor, the Universal Child Care Benefit, was taxable and had to be deducted under Schedule III, but the UCCB ended in 2016.

Can child support be based on something other than my tax return? Yes. If Line 15000 is not the fairest measure, section 17 lets a court look at your last three years and smooth out swings or one-time amounts. Section 18 can add corporate pre-tax income for shareholders, and section 19 lets a court impute income, for example when a parent is intentionally under-employed.

Do I have to send my ex my tax return every year? If there is a child support order, section 25 says the payor must provide income documents on the other parent's written request, no more than once a year. That means tax returns and notices of assessment for the three most recent years not already provided, plus updates on Section 7 expenses.

Where to start this week

Pull your last notice of assessment and find line 15000. Then go down the Schedule III list and mark the three or four items that could apply to you: union dues, dividends, capital gains, CCA on a rental. If none apply, congratulations, your Guidelines income is your line 15000 and the hard part is over. If two or three apply, that's your conversation with a lawyer, and now you'll know what to ask.

Then do the other half, the part no regulation handles: start logging what you're both actually spending on the kids. The income percentage is only useful when there's an honest total to apply it to.

CoParentSplit tracks shared child expenses, calculates who owes what, and notifies the other parent so you don't have to send that text. It's $6.99 a month or $59.99 a year, and that covers both parents, not each. The free tier handles 10 expenses a month if you want to test it before paying for anything. You can also run the numbers first with the free expense calculator.

Stop fighting about money. Start tracking it.

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Related: Child Support vs Shared Expenses: What's the Difference in Canada? · Co-Parenting Tax Deductions 2026 · What to Do When a Co-Parent Won't Split Expenses