Introduction

Corporate tax instalments operate on a fixed calendar regardless of how uneven a contractor's revenue is during the year. For a construction company that earns most of its revenue between May and October and faces a quiet winter, making equal monthly instalments based on the prior year's tax can create cash flow pressure in the low-revenue months — and potentially an overpayment in years where revenue falls short of the prior year.

Understanding the instalment calculation options, and using the one that best matches the actual business cycle, is a practical planning tool for seasonal construction businesses.

Recap: How Corporate Instalments Are Calculated

As discussed in Article 51, there are three methods for calculating instalment amounts:

Method 1 — Prior year tax: Pay 1/12 of the prior year's net corporate tax owing each month (or 1/4 each quarter for eligible corporations). This is the most common approach for most corporations.

Method 2 — Prior year and current year blend: Use the second prior year's tax for the first two monthly instalments, then switch to 1/10 of the estimated current year tax for the remaining ten.

Method 3 — Current year estimate: Base all instalments on the current year's estimated income. If the estimate is accurate, no instalment interest applies. If the estimate is too low, interest charges accrue from the dates instalments were due.

The Seasonal Problem With Method 1

For a construction company whose revenue peaked in the prior year but is experiencing a slower current year, Method 1 results in monthly instalments based on last year's income — which may be significantly higher than the current year's income supports.

The cash flow effect is particularly acute in winter months when revenue is low but instalment payments based on last year's strong summer are still due.

How Method 3 Helps Seasonal Businesses

Method 3 — basing instalments on the current year's estimated income — allows a contractor to reduce instalments during slow months and increase them during active months, provided the total instalments for the year are sufficient to cover the actual tax liability.

For example, a contractor who estimates their current year's tax at $60,000 (versus $90,000 in the prior year) can reduce each monthly instalment from $7,500 (under Method 1) to $5,000 (under Method 3). The annual total still covers the liability, and the monthly payments are more aligned with actual cash flow.

The risk with Method 3 is precision. If the year-end income turns out higher than estimated and the instalments based on the lower estimate are insufficient, interest accrues on the shortfall from the date each instalment was due. This is not a penalty — but the interest can be meaningful if the estimate is significantly low.

Mid-Year Recalibration

For contractors using Method 3, a mid-year review — ideally in September or October when the active season's results are becoming clear — allows the instalment estimate to be adjusted for the remaining months. If year-to-date income is tracking ahead of the estimate, increasing the final instalments can prevent a large interest charge from a shortfall.

This mid-year recalibration is one of the clearest examples of how an advisory CPA relationship (reviewing the corporate position during the year, not just at year end) produces better outcomes than a once-a-year filing engagement.

The Year-End Balance Timing

Even with well-managed instalments, there is typically a final balance due at the two-month (or three-month, for qualifying CCPCs) mark after fiscal year end. For a December 31 year-end construction company, the balance is due by the end of February or March — before the T2 is even filed in June.

Contractors who have not tracked their year-to-date income position may be surprised by a large balance owing in February. Building a tax reserve from strong project months — as discussed in Article 64 — is the practical solution.

When to Speak With a CPA

For construction companies with significant seasonal variability, annual instalment planning — including reviewing which calculation method produces the lowest interest-adjusted cost — is worth a specific conversation. The right method is not always Method 1, and the difference can be significant in transition years.

Rotaru CPA works with incorporated contractors on tax instalment planning and year-round cash flow management. Book a consultation to review your instalment position.