Missed the September 15 CRA Instalment? What Happens Now (2026)

If the September 15, 2026 CRA instalment date passed and you didn't pay — or paid less than required — nothing dramatic happens automatically. What starts is instalment interest: the CRA charges it on the shortfall at the prescribed rate, compounded daily, from September 15 until you pay or until your balance due date. The confirmed rate is 7% for the third quarter of 2026 (July 1–September 30) and 7% again for the fourth quarter (October 1–December 31), so one flat rate covers the whole catch-up window. This is a calm walk through what actually happens, what it costs, and exactly how to catch up before the December 15 date.

First: nothing happened on September 16

There is no default flag, no collections call, no letter that goes out the day after a missed instalment. What exists instead is a running interest calculation the CRA applies when it processes your 2026 return: for every day an instalment was unpaid or short, interest accrues on that amount at the quarter's prescribed rate. It compounds daily — each day's interest is added to the balance before the next day's interest is calculated — so the cost grows faster the longer the gap runs, but it is still just interest, not a penalty, until a separate threshold is crossed (more on that below).

The rate that applies to your September shortfall

The confirmed CRA prescribed interest rate on overdue amounts — including late or short instalments — is 7% for the third quarter of 2026, July 1 to September 30 (Canada Revenue Agency). That rate covers every day your September 15 instalment sat unpaid through September 30. The CRA has confirmed the same 7% rate for the fourth quarter of 2026, October 1 to December 31 — unchanged from Q3. So whether you clear the shortfall this week, in October, or right at the December 15 date, every day of the gap is charged at one flat 7%, compounded daily, with no quarter-boundary adjustment to make. (Only days that slip into 2027 would run at a Q1 2027 rate, which the CRA has not set yet.)

The part that softens the picture: contra interest

Instalment interest is not evaluated on September 15 in isolation. The CRA calculates your instalment interest charge as the interest on instalments you should have paid, minus credit ("contra") interest on instalments you did pay early or over the required amount (Canada Revenue Agency). So if you paid March or June in full or ahead of schedule, that built up credit interest that nets against what September now owes. If you're able to pay December 15 a little early or a little over the required amount, that also builds credit that can offset outstanding interest elsewhere in the year. The credit is not refundable and can only be applied against interest charges for the same tax year — it isn't cash back — but it is a real offset, not a rounding footnote, and it's the CRA's own mechanism rather than an unofficial workaround.

When a real penalty gets added — and when it doesn't

Interest and the instalment penalty are two separate things, and most people never reach the second one. An instalment penalty applies only if your total 2026 instalment interest charges exceed $1,000. Below that line, whatever interest accrued is the entire cost of being late — nothing else is added.

When the $1,000 line is crossed, the formula is specific: the CRA takes the greater of $1,000 or 25% of the interest you would have paid had you made no instalment payments at all that year, subtracts that figure from your actual instalment interest, and divides the difference by two (Canada Revenue Agency). The CRA's own example makes the shape concrete: with $2,500 of actual instalment interest, the flat $1,000 threshold applies (it's larger than 25% of the no-payments figure in that example), giving ($2,500 − $1,000) ÷ 2 = a $750 penalty. For someone whose instalment interest for the year is in the hundreds, not thousands, this formula simply doesn't come into play.

A worked example: a $2,500 missed September instalment

Say your September 15, 2026 instalment was $2,500 and you're only now, on September 21, getting around to paying it — six days late so far, at the confirmed 7% Q3 rate:

Item	Amount
Instalment missed	$2,500
Days late so far (Sept 15 → Sept 21)	6 days
Rate for those days (confirmed Q3 2026)	7%, compounded daily
Interest accrued so far	≈ $2.90

Six days in, the cost is genuinely small — a few dollars. The number that matters is how long you let the gap run. Left unpaid all the way to the April 30, 2027 balance due date — 227 days total, at the confirmed 7% — confirmed through the end of 2026, with the 2027 quarters not set yet, so treat the tail of that run as an illustration — the same $2,500 would accrue roughly $111 in instalment interest, nowhere near the $1,000 penalty threshold. The arithmetic scales with days, not with drama: paying this week instead of in December, and December instead of next April, is the entire lever you control.

The three ways you (or CRA) calculated what you owed — and why it matters now

Every instalment amount comes from one of three methods, and knowing which one applied to your September payment explains why the shortfall happened and what your risk looks like for December:

Option	How it's calculated	Risk if you underpay
No-calculation option	CRA works it out from your latest assessed return and prints the amount right on your instalment reminder.	Lowest risk — if you pay exactly the reminder amount by each date, the CRA does not charge instalment interest or a penalty even if it turns out too low for your real 2026 tax owing.
Prior-year option	You calculate instalments based on your 2025 assessed tax return instead of the reminder amount.	Same protection applies only if your estimate is accurate enough to cover what you actually owed — pay less than required and interest accrues on the shortfall.
Current-year option	You estimate your 2026 net tax owing, CPP contributions, and voluntary EI premiums directly.	Most exposure: if your 2026 income comes in higher than estimated, the shortfall (and its interest) reflects the gap between your estimate and reality.

Choosing a lower option than the no-calculation amount is entirely allowed — it's designed for people whose income genuinely dropped — but it shifts the risk onto your own estimate. If September was based on a current-year guess that came in low, that's the shortfall now generating interest. It's a reasonable trade if your income really did fall; it's worth revisiting before December 15 if it didn't.

How to actually pay the catch-up, today

Three ways reach the CRA before December 15 if you act this week:

• CRA My Payment — a one-time online payment straight from your bank account. Debit card only; the CRA is explicit that you cannot use a credit card with My Payment.
• Online banking bill payment — add the CRA as a payee the same way you'd pay a utility bill, using your specific instalment account.
• Pre-authorized debit (PAD) — set up in CRA My Account for a direct withdrawal on a date you choose. It must be scheduled at least 5 business days before the money comes out, so if you want it done by a specific date, set it up now, not the day before.

Whichever method you use, catching up sooner rather than later is the one variable that actually reduces what you owe — every day earlier is a day less compounding.

Québec residents: a lower bar

If you live in Québec, the threshold that determines whether instalments apply to you at all is $1,800 in net tax owing, not $3,000 — tested the same two-year way (2026, and either 2025 or 2024). If your 2026 net tax owing is at or under $1,800, September 15 likely never applied to you in the first place, whatever a reminder implied. See our full breakdown of the Québec $1,800 threshold before assuming the instalment system applies to you.

Set up December 15 while you're already here

The cheapest fix for the same problem happening again in three months is doing it now: schedule the December 15 amount today, whether that's a PAD you set up in one sitting or a calendar reminder with the money already set aside in a tax jar. Our CRA instalment calculator will show your own per-quarter figure and current due dates, and the mechanics of the interest itself are covered in full in our instalment-interest deep dive if you want the complete math behind the daily-compounding rate.

Sources

• CRA — Prescribed interest rates, third calendar quarter 2026 (7% on overdue amounts, July 1–September 30, 2026)
• CRA — Prescribed interest rates, fourth calendar quarter 2026 (7% on overdue amounts, October 1–December 31, 2026)
• CRA — Interest and penalty charges on instalments (daily compounding; contra/credit interest for early or overpaid instalments; the $1,000 penalty threshold and formula)
• CRA — Who has to pay tax instalments ($3,000 / $1,800 Québec thresholds; the two-part 2026-and-2025-or-2024 test)
• CRA — Calculation options for instalment payments (no-calculation, prior-year, current-year)
• CRA — Make a payment (My Payment debit-only rule; online banking; pre-authorized debit and its 5-business-day scheduling requirement)

This article explains CRA rules in plain language. It is general information, not tax advice for your situation — every figure above was verified against canada.ca on 21 September 2026. Rules, thresholds, and quarterly rates change; check the current CRA page before relying on a number.