Most of the stress around tax season is not the tax. It's the not knowing — which deadline is yours, whether the date you're thinking of is the filing date or the payment date, and what happens if the two aren't the same. Here is the plain version for Ontario small businesses and the people who run them. It won't replace a conversation about your specific situation, but it will tell you what to look for.
Personal filing (T1)
If you earn employment or investment income, your personal T1 return is due at the end of April, and any balance you owe is due the same day. That second part is the one people miss: even if you file early, interest starts on an unpaid balance from the payment deadline, not from when you got around to filing.
Filing on time even when you can't pay in full still matters. The late-filing penalty and the interest on an unpaid balance are two separate things — you can avoid the first while you sort out the second.
Self-employed
If you or your spouse are self-employed, you get extra time to file — into the middle of June — but the payment deadline does not move with it. Any balance owing is still due at the end of April.
The self-employed filing date and the payment date are different. Plan around the earlier one.
In practice that means estimating what you'll owe before the April payment date, even though your return isn't due yet. It's the single most common surprise for people in their first year of self-employment.
Corporate (T2)
A corporation's deadlines are tied to its fiscal year-end, not the calendar. The T2 return is generally due six months after your year-end. The balance owing is due earlier than that — usually two months after year-end, with an extra month available to some Canadian-controlled private corporations that meet the conditions.
Because these dates float with your year-end, two corporations can have completely different deadlines in the same month. If you've just incorporated, the first thing worth pinning down is your year-end — everything else follows from it.
HST/GST
Your HST/GST filing frequency is assigned based on your revenue, and it changes as you grow. Smaller businesses often file annually; past certain thresholds the CRA moves you to quarterly, and larger filers report monthly.
The rule of thumb: annual filers generally report a few months after their fiscal year-end, quarterly and monthly filers roughly one month after each period closes. The exact dates depend on your assigned frequency, so confirm which one you're on before you set reminders — being on the wrong assumption is how a filing quietly slips.
Payroll remittances
If you have employees, the deductions you withhold — income tax, CPP, EI — have to be remitted to the CRA on a schedule set by how much you remit. Most small employers are regular remitters, due by the 15th of the month after the payroll. Higher-volume employers are put on accelerated schedules.
Year-end payroll slips — the T4s that go to your staff and to the CRA — are due at the end of February. Missing that date carries per-slip penalties that add up quickly for even a small team.
Instalments
Instalments are pre-payments toward a bill you haven't been assessed yet. They apply when your balance owing was over the CRA's threshold in the prior year (and is expected to be again), and they're generally due quarterly — mid-March, June, September, and December.
They apply to individuals and corporations both. If you've never paid by instalment and suddenly get a reminder notice, that's the CRA telling you last year's balance crossed the line — it's worth a call before the first one is due.
What actually happens if you miss one
Missing a deadline is not a crisis, but ignoring it is expensive. Late filing generally triggers a penalty calculated on the balance owing, and interest accrues on unpaid amounts, compounding daily. The penalty for filing late a second time within a short window is steeper — the CRA treats repeat lateness differently from a one-off.
The practical advice is boring and correct: file on time even if you can't pay, pay what you can toward the balance, and talk to someone before the notice becomes a bigger number. In many cases relief provisions exist for genuine hardship or a first mistake — but you have to ask, and the details matter, so we won't pretend to know your case from a blog post.
If you'd rather not track any of this yourself, that's the job. We keep your dates, file on time, and tell you what's coming before it arrives.
See the full reference, or let us map your specific filing calendar.