Corporate Tax Instalments and Deadlines for Ontario CCPCs: A Practical Guide

Paying corporate income tax is not a once-a-year event. Like individuals with significant income, most Canadian corporations — including Ontario CCPCs — must pay tax instalments throughout the year rather than in one lump sum when the return is filed. Miss an instalment or underpay, and the CRA charges interest from the date the payment was due. That interest is not deductible as a business expense, so it is pure dead money.

Understanding when instalments are due, which calculation method to use, and how to avoid the most common traps is practical knowledge for every Ontario business owner and their bookkeeper. Confirm current figures and rates with the CRA and your accountant — deadlines and interest rates are set by regulation and can change.

Who Must Pay Corporate Tax Instalments?

Your corporation must pay instalments if its total tax payable (federal plus provincial, net of any applicable credits) for the current year or the immediately preceding year will exceed a defined threshold. As of writing, that threshold is set by the Income Tax Act; verify the current figure with the CRA.

Corporations below the threshold can pay their entire tax bill on the balance-due date without facing instalment interest.

Most active Ontario CCPCs earning meaningful profits will exceed the threshold and must pay monthly or quarterly instalments. Confirm with your accountant at the start of each fiscal year whether instalments are required.

When Are Instalments Due?

Monthly Instalments

Most corporations pay monthly instalments — one payment per month, every month of the tax year, due on or before the last day of each month.

Quarterly Instalments (Small CCPCs)

A qualified small CCPC may be eligible to pay quarterly rather than monthly instalments. This applies if the corporation's federal tax payable in the current and previous year did not exceed a defined amount and if certain other conditions are met (for example, a good instalment compliance history). As of writing, the threshold and conditions are set by the Income Tax Act; confirm eligibility with your accountant. Quarterly payments are due on or before the last day of March, June, September, and December for a December 31 year-end.

Three Methods for Calculating Instalment Amounts

The CRA gives corporations three acceptable methods for calculating how much to pay each instalment period. Choosing the right one can avoid overpaying (a cash flow cost) or underpaying (triggering interest).

Method 1: Prior Year's Tax

Pay one-twelfth (for monthly) or one-quarter (for quarterly) of the previous year's net tax payable. This is simple and safe — if you pay based on last year's actual liability, the CRA will not charge instalment interest even if you end up owing more in the current year.

Method 2: Estimated Current Year Tax

Pay one-twelfth or one-quarter of what you estimate your current year tax will be. This is useful if you expect this year's income to be significantly lower than last year. If your estimate is right, you do not overpay; if you underestimate, you will owe instalment interest.

Method 3: Two-Year Averaging (Federal Only)

A hybrid: base the first two instalments on two years prior, then pay the rest based on the current year estimate. This is most useful for corporations with volatile income.

In practice, most accountants recommend starting with the prior-year method (Method 1) to guarantee no instalment interest, then adjusting if the current year's income is clearly lower.

The Corporate Tax Return Filing Deadline

The T2 corporate income tax return is due six months after the end of the corporation's taxation year. For a December 31 year-end, the T2 is due June 30 of the following year. For a March 31 year-end, the T2 is due September 30.

However — and this is the trap many new business owners fall into — the balance of tax due is payable within two months (three months for eligible CCPCs) after the year-end, not six months. So for a December 31 year-end:

• Balance of tax owing: February 28 (or March 31 for eligible CCPCs as of writing — confirm current rules)
• T2 return filing: June 30

If you wait to calculate what you owe until you file the T2 in June but your tax was due in February, you have accrued several months of arrears interest. File the balance-of-tax calculation early, even if you file the return later.

Instalment Interest: How It Works

If you miss an instalment or pay less than required, the CRA charges interest at the prescribed rate (updated quarterly) from the date the instalment was due to the earlier of the date you pay or the balance-due date. The prescribed rate on overdue taxes is generally the basic rate plus a premium — confirm the current rate at the CRA's website or with your accountant.

The CRA also calculates whether your actual instalments were sufficient using the most favorable of the three methods — so you only pay interest if you underpaid under all three methods. This helps corporations that underpaid because income was lower than expected.

Ontario Provincial Corporate Tax

Ontario no longer administers its own corporate income tax separately — Ontario corporate income tax is administered by the CRA as part of the federal-provincial integration. This means a single T2 return covers both federal and Ontario tax, and instalments paid to the CRA satisfy both obligations. You do not file a separate Ontario return for the basic Ontario corporate income tax.

Frequently asked questions