October 31 Is More Than Halloween: Ontario Quarterly HST Filers, This One's for You

Your Q3 HST return is due in one week — here's exactly what that means and what to do if you're not ready

Every year, October 31 surprises Ontario business owners in two ways simultaneously. First, because it falls on a holiday weekend, it feels like a day off rather than a filing deadline. Second, because Q3 — July, August, and September — includes the summer months when bookkeeping often falls behind.

The combination is expensive. CRA's penalty for late HST remittance starts at 3% of the amount owing and rises to 10% for repeated late filings within a twelve-month window. For a business remitting $15,000 in quarterly HST, a 10% penalty is $1,500 in a single instance.

This post is for every Ontario quarterly HST filer who needs to know exactly what to do in the next seven days.

Who Is a Quarterly HST Filer?

CRA assigns HST filing frequency based on your annual taxable revenues. Quarterly filing applies to businesses with annual taxable revenues between $1.5 million and $6 million. It also applies to smaller businesses that have opted into quarterly filing rather than annual.

If you are not sure of your filing frequency, log into CRA's My Business Account and check your GST/HST account settings. Your filing frequency determines both what you owe and when you owe it.

What Q3 Covers

The Q3 reporting period for calendar-year quarterly filers covers July 1 through September 30, 2026. Every taxable sale made during those three months generated HST at 13% in Ontario — and that HST must be reported and remitted to CRA by October 31.

But you do not remit the full HST collected. You remit the net amount: HST collected on your sales minus the Input Tax Credits (ITCs) you are entitled to claim on your business purchases.

How to Calculate Your Net HST Owing

The calculation has two components:

• HST collected: the total Ontario HST charged on all taxable sales and services invoiced during July, August, and September. If your books are current, this number comes directly from your HST-collected account.

• Input Tax Credits (ITCs): the HST you paid on business expenses during the same period. ITCs reduce your remittance dollar for dollar. To claim an ITC, you need a valid invoice showing the vendor's HST registration number (for purchases over $30), the date, the amount, and the HST charged.

• Net HST owing equals HST collected minus ITCs. If your ITCs exceed your HST collected — common for businesses with high input costs or that are in a growth phase — the result is a refund, not a payment.

The Electronic Filing Requirement

All GST/HST registrants with annual revenues above $1.5 million are required to file electronically. Paper filing is no longer an option for most Ontario quarterly filers — and submitting a paper return when electronic filing is required triggers an automatic $100 penalty for the first offence and $250 for subsequent offences.

Electronic filing is done through CRA's My Business Account portal, which also allows direct payment. The filing and payment must both be received by CRA by October 31 — filing on time and paying late still generates interest from the due date.

The 5 Most Common Q3 HST Errors

1. Claiming ITCs without valid invoices. A bank statement showing a purchase is not sufficient. The invoice must show the vendor's HST number for purchases over $30.

2. Missing HST on taxable sales. Every taxable sale generates HST. If invoices were issued without HST — particularly for newer customers or one-time sales — those amounts may still be owed.

3. Including HST on exempt supplies. Some supplies are HST-exempt. Remitting HST you were not required to collect does not hurt you, but overclaiming ITCs on exempt inputs creates an assessment risk.

4. Reporting on a cash basis rather than an accrual basis. HST is generally reportable when invoiced, not when paid. If your books are on a cash basis but your HST should be on an accrual basis, the Q3 filing may be understated.

5. Forgetting to include the HST rebate recovery. If your organization claimed a public service bodies' rebate in the prior year, certain adjustments may be required in the current year's return.

What Happens If You Miss October 31

Missing the October 31 deadline triggers an immediate late-filing penalty of 3% of the net tax owing, plus 1% for each additional month, up to a maximum of 12 months. A previous late filing within the past 12 months doubles the penalty rate.

Interest also accrues daily from October 31 on any unpaid balance, at CRA's prescribed rate plus an additional 4%.

If your bookkeeping is not ready to support an accurate filing, file an estimated return by October 31 and amend it once your books are reconciled. Filing something — even an estimate — stops the late-filing penalty clock. Owing interest is far less expensive than owing a penalty on top of interest.

How Monthly Bookkeeping Makes This a 15-Minute Task

For Ontario businesses with current, monthly books, Q3 HST filing takes roughly fifteen minutes. The HST collected figure is already in the accounting software. The ITC total is already reconciled. The net owing is calculated automatically.

The filing itself — through My Business Account — takes about ten minutes. The payment clears immediately through online banking.

For businesses without current books, the same process takes several hours or several days, after spending additional time reconstructing three months of transactions that should have been recorded monthly.

Is your Q3 HST ready? Metarithmika helps Ontario businesses stay current with every HST obligation, every quarter.

Book a free discovery call. metarithmika.ca

Official CRA sources:

canada.ca — GST/HST filing and payment deadlines

canada.ca — Input tax credits (CRA)

Client's Guarantee

Referral Program

Client's Onboarding Process

Frequent Questions & Answers