How the calculation works
On Form ON428 you add a basic reduction ($294 on the 2025 form) to $544 for each dependent child born in 2007 or later and $544 for each dependant with a mental or physical impairment you are claiming an amount for. That total is doubled, and your Ontario tax is subtracted. If the result is positive, it is your reduction.
Because your own tax is subtracted from double the total, the reduction shrinks as Ontario tax rises and disappears once your tax equals double the total. It is applied after the surtax and before the Ontario health premium, so it does not lower the premium.
An illustrative example
A single person with no dependants has a total of $294, doubled to $588. If Ontario tax is $200, the reduction is $388, which is more than the tax, so Ontario tax falls to zero. If Ontario tax is $400, the reduction is $188 and Ontario tax becomes $212. At $588 or more, there is no reduction.
A parent with one dependent child has $294 plus $544, or $838, doubled to $1,676. With Ontario tax of $1,000, the reduction is $676 and tax falls to $324. These are round, illustrative numbers using the 2025 amounts. They are not a forecast of any person’s return.
Who can and cannot claim it
You must have been a resident of Canada at the beginning of the year and a resident of Ontario on December 31. It is not available if alternative minimum tax applies and creates Ontario additional tax, or if you were bankrupt at any point in the year. You may also choose not to claim it. A final return for someone who died can claim it as if they were single.
The dependent child and impaired dependant amounts can be claimed by only one person. If you had a spouse or common-law partner on December 31, it is the partner with the higher net income on line 23600. A dependent child must generally be 18 or younger at year end, have lived with you and be your or your partner’s child, with a couple of exclusions listed on the form guide. It is separate from the LIFT credit, which has its own conditions.
What to discuss with your accountant
Return software usually applies the reduction automatically, so the useful questions are about the inputs. Confirm which spouse claims the children, that each child’s birth year and residence qualify, and that any impairment-related claims are consistent across the return.
Bring both partners’ net income, children’s birth dates and any notices of assessment. If a minimum tax calculation applies in a year, ask how that affects the reduction. The Ontario surtax and health premium are covered in their own entries.
Sources & editorial notes
Sources checked October 24, 2026. The examples are illustrative and provide general information. Discuss how the guidance applies to your circumstances with your accountant.
- Ontario tax information for 2025Canada Revenue Agency
- Form ON428, Ontario Tax (2025)Canada Revenue Agency
Rules and guidance can change. Use the current official source and confirm the treatment for your facts. To flag an error, contact Sora.