Are Your Tax Instalments Too High or Too Low? How to Adjust Before the Surprise

The CRA does not send you a bill for instalments. It sends you an estimate of the business you used to be.

That is the whole problem in one sentence. Instalment amounts are built from a year that has already closed. The payments come out of a business that is living in this one. Most of the time the two are close enough that nobody looks. In the years they are not close - the year revenue dropped, the year a contract doubled, the year you sold something - the gap runs for twelve months before anyone notices.

Both directions cost money. They just cost it differently. Overpaying is quiet: your cash sits with the CRA until a refund is issued. Underpaying is expensive: instalment interest compounds daily, and past a certain point a penalty is added on top.

The next personal instalment is due September 15. Corporate instalments are due monthly or quarterly, depending on the corporation. Either way, this is still a decision rather than a discovery.

Who Actually Has to Pay Instalments?

Three separate systems, three separate sets of rules. Owners of incorporated businesses are usually in at least two of them at the same time.

Personal income tax. You are required to pay instalments where your net tax owing is above the threshold in the current year and in either of the two previous years. The federal threshold is $3,000 ($1,800 for Quebec residents). This is what catches self-employed people, owners paid in dividends, and anyone with meaningful investment or rental income. The common factor is income with no tax withheld at source.

Corporate income tax. A corporation generally pays monthly instalments where its total taxes payable for the current or previous year exceed $3,000. Eligible CCPCs can pay quarterly instead, provided they claim the small business deduction and meet the taxable income, taxable capital, and compliance conditions. A corporation in its first year of existence generally has no instalment obligation, because there is no prior year to calculate from, which is exactly why the second year surprises people.

GST/HST. A separate obligation with its own calendar. Annual filers whose net tax for the previous fiscal year met the threshold pay quarterly instalments, due one month after each fiscal quarter ends.

Thresholds and prescribed rates change. Confirm the current figures at canada.ca before you calculate against them.

The Three Ways to Calculate, and Why the Default Is Not Always Right

For personal instalments, the CRA offers three methods. You are allowed to choose, and the choice is not announced anywhere.

The no-calculation option. You pay exactly what the CRA's instalment reminder tells you to pay, on the dates shown. The reminder is built from your previously assessed returns. The advantage is protection: pay the reminder amounts in full and on time and no instalment interest applies, even if you end up owing more.

The prior-year option. You base instalments on last year's net tax owing, split across the year. Useful when this year looks like last year but the reminder was built from a year further back.

The current-year estimate option. You base instalments on what you expect to owe this year. This is the one that saves money in a down year, and the one that carries risk. If the estimate is too low, interest applies on the shortfall as though you had never adjusted.

Corporations have a parallel set of choices: estimated tax for the current year, tax payable for the prior year, or a hybrid where the first instalment is based on the second-preceding year and the remainder on the prior year. The hybrid exists because a corporation often does not know its prior-year figure by the time the first payment comes due.

There is no method that is correct for every business. There is a method that is correct for your year, and it is identifiable now, when six months of data exist.

What Overpaying Actually Costs

Nothing dramatic happens when you overpay. That is why it goes unfixed for years.

Say a corporation's instalments were set from a strong prior year, and revenue is down 30% this year. Every month, a payment sized for a business that no longer exists leaves the account. The money is not lost. It comes back as a refund after the return is assessed, which for a corporation with a December year-end means the money returns well into the following year.

In the meantime that cash was not available for payroll, inventory, or a line of credit you would rather not draw on. The CRA does pay interest on overpayments, at a prescribed rate that is set below the rate it charges. Whether that partially offsets the cost is a question of what the money would have done in the business.

This is a working capital problem wearing a tax costume. The fix is not complicated: recalculate on current-year figures and stop financing the government at a rate you did not agree to.

What Underpaying Actually Costs

The other direction has a meter running.

Instalment interest is charged on late or insufficient instalment payments, calculated from the day each payment was due, compounded daily at the CRA's prescribed rate for overdue amounts. The clock does not wait for the return.

On top of that sits the instalment penalty. It applies where instalment interest for the year exceeds $1,000, and it is calculated as half the amount by which the interest exceeds that figure. Small shortfalls generate interest only. Large ones generate interest plus penalty. Confirm the current prescribed rate at canada.ca.

Instalment interest works on an offset basis within the year. Interest earned on early or overpaid instalments can reduce interest charged on late or short ones.

That mechanic is worth knowing because it is genuinely useful. An owner who realizes in September that the first two payments were light can make up ground by paying more, and earlier, on the remaining ones. It does not eliminate a shortfall, but it reduces it, and it only works if you act before the year closes.

The Five Situations That Break the Assumption

Instalments are wrong in predictable circumstances. If any of these apply to your year, the calculation needs to be rerun rather than assumed.

• Revenue moved materially in either direction. A 20% swing over six months is enough to make prior-year instalments the wrong size.
• You had a one-time event last year. A property sale, an asset disposition, a single unusually large contract. The instalments built from that year assume it repeats. It does not.
• Your remuneration mix changed. Moving from salary to dividends removes withholding at source and moves the obligation into personal instalments. The corporation's position changes at the same time.
• You incorporated partway through. Personal instalments built from your sole-proprietor years keep arriving while income now flows through a corporation with its own obligation.
• It is your corporation's second year. No instalments were required in year one. Year two brings a full schedule, and it is often the first time an owner is asked to pay tax before the return is filed.

How to Adjust, Practically

None of this requires waiting for year-end.

• Reconcile through June. Every calculation here depends on numbers that are current. Books that are two months behind produce an estimate that is confidently wrong.
• Project the full year from actuals. Six months of reconciled data plus a known second half. Not a forecast, and not last year with a percentage added to it.
• Compare against what you have already paid. Total instalments to date versus total estimated tax for the year, prorated to where you are in the calendar. This single comparison tells you which of the two problems you have.
• Adjust the remaining payments, and document the basis. If you switch to the current-year estimate, keep the working papers showing how the estimate was built. If the number is later questioned, the calculation is the answer.

If the review shows you are behind, pay more on the next scheduled instalment rather than waiting for the return. The offset mechanic makes earlier money worth more than later money.

The Dates

The next personal instalment is September 15. A corporation on a monthly schedule has already made six or seven payments this year on numbers set last year.

How Count myAccount Handles This

Instalment position is part of the reporting cycle Count myAccount runs, not a calculation that happens when an owner thinks to ask for it.

• Your file is assigned to a specialist who works with your business size and structure regularly.
• We reconcile your bank and credit card accounts monthly, so an instalment review runs on current figures rather than reconstructed ones.
• Instalment obligations across corporate tax, personal tax, and GST/HST are tracked against your fiscal calendar and flagged before each due date.
• Where the year has moved away from the prior-year basis, we run the current-year calculation and show you both numbers before anything is filed or paid.
• The basis for any adjustment is documented at the time it is made, not reconstructed later.

Clear steps. No surprises.

Frequently Asked Questions

Do I have to pay tax instalments in Canada?

For personal income tax, instalments are required where your net tax owing exceeds $3,000 ($1,800 for Quebec residents) in the current year and in either of the two previous years. A corporation generally pays monthly instalments where total taxes payable exceed $3,000 in the current or previous year, with a quarterly option for eligible CCPCs that meet the small business deduction and related conditions. GST/HST instalments are separate again, applying to annual filers above the net tax threshold. Confirm current thresholds at canada.ca.

Can I lower my tax instalments if my income dropped?

Yes. You can base instalments on an estimate of the current year rather than a prior-year figure, and you can make that change partway through the year. This stops you from prepaying tax you will not owe and waiting for a refund to recover it. The risk sits entirely on the accuracy of the estimate: if it turns out to be low, instalment interest applies on the shortfall as though no adjustment had been made. Build the estimate from reconciled six-month actuals, not from a projection.

What happens if I do not pay my tax instalments?

Instalment interest is charged from the date each payment was due, compounded daily at the CRA's prescribed rate for overdue amounts. Where instalment interest for the year exceeds $1,000, an instalment penalty is added, calculated as half the amount above that figure. Interest starts accruing well before the return is filed, which is why a shortfall found in August costs less than the same shortfall found in April.

Can I catch up on instalments I missed earlier in the year?

Partly, and it is worth doing. Instalment interest is calculated on an offset basis within the year: interest earned on early or overpaid instalments reduces interest charged on late or insufficient ones. Paying more, and earlier, on the remaining instalments reduces the total interest even though it does not erase the original shortfall. The mechanic only works within the year, so it rewards acting in September rather than waiting for the filing.

What is the no-calculation option?

It is the method where you pay exactly the amounts shown on the CRA's instalment reminder, on the dates shown. The amounts are calculated by the CRA from your previously assessed returns. The advantage is protection: if you pay those amounts in full and on time, no instalment interest is charged even if your actual tax for the year turns out to be higher. The disadvantage is that the reminder is built from the past, so in a year where income has fallen it will have you prepaying tax you do not owe.

Do I pay instalments in my corporation's first year?

Generally no. Instalment calculations are based on tax payable in a prior year, and a corporation in its first year does not have one. The obligation typically appears in year two, which is when many owners are asked to pay corporate tax before filing a return for the first time. It is worth planning for during year one rather than discovering with the first reminder.

Are GST/HST instalments the same as income tax instalments?

No. They are a separate obligation with a separate calendar, applying to annual GST/HST filers whose net tax for the previous fiscal year met the threshold. Instalments are due one month after the end of each fiscal quarter, with any balance settled when the annual return is filed. An owner can be current on corporate income tax instalments and behind on GST/HST instalments at the same time, because nothing connects the two schedules.