Invoicing Software for Ontario Accounting Firms

How does invoicing software work for firms in Ontario?

The CRA administers Ontario's HST — one registration, one return. Ontario clients file a single 13% HST return with the CRA rather than separate federal and provincial sales-tax returns.

An Ontario firm's own invoices carry 13% HST, and so does the fee schedule inside an engagement letter. Pricing the engagement in writing before the work starts is what makes the eventual invoice a formality rather than a negotiation.

Which CRA deadlines apply?

These rules are federal and apply in every province and territory. Where a due date falls on a weekend or public holiday, the CRA treats the next business day as on time — compute the shifted date each year rather than carrying the calendar forward.

What is different about running a practice in Ontario?

Four things a firm working Ontario files should be able to state without looking them up. Each is verified against a primary source, linked at the foot of this page.

CPA Ontario is the provincial body; 410,154 of Ontario's 418,322 employer businesses were small businesses as of December 2024.

• Canada's largest market for accounting services — Ontario had 410,154 small employer businesses as of December 2024 — more than Quebec and British Columbia combined. Every one of them is a potential compliance client.
• One 13% HST return — Ontario harmonized its provincial sales tax with the GST, so Ontario businesses charge 13% HST and file one sales-tax return with the CRA instead of two.
• Small-business rate dropping in 2026 — Ontario's provincial small-business rate is 3.2% and falls to 2.2% effective July 1, 2026, which affects year-end planning for corporations straddling that date.
• An Employer Health Tax to watch — Ontario levies an Employer Health Tax on payrolls above an exemption threshold, so Ontario payroll clients carry a provincial obligation on top of CRA source deductions. Confirm the current rate and exemption with the Ontario Ministry of Finance before advising.

Managing invoicing software across a client book in Ontario

A firm's billing problem starts before the invoice: unless scope and price were agreed in writing, every bill is a negotiation.

A three-partner Mississauga firm with roughly 220 T1 clients and 45 corporate year-ends spread across the calendar never has an off-season. April 30 is the visible crunch, but the quieter risk is the corporate file whose year-end was in September: the T2 is due in March, the balance was due in December, and nothing on a calendar-year spreadsheet says so. Fiscal-year-end-driven reminders are what close that gap.

How SpidNums handles it

SpidNums models the firm as clients, services and work. Assigning a typed service to an Ontario client is what generates the recurring projects, the stages and the reminders — the cadence is recorded once rather than remembered each period.

Every open obligation is then ranked by how close its due date sits and coloured accordingly, so the morning question — what is late, what is close, what is fine — is answered by looking.

• Services catalogue with per-service pricing lines
• Engagement letters built from assigned services or prior-year history
• Firm letterhead and branding on every client-facing document
• Client e-signature by type, draw or upload on a no-login page
• Signed PDF stored on the client record
• Annual renewal prompts when scope changes

Where this goes wrong

Billing failures start upstream of the invoice. By the time a fee is being argued about, the mistake was made months earlier.

• The engagement letter is a copy of last year's, so this year's expanded scope is unpriced.
• A client is asked to create an account to sign, and simply does not sign.
• Out-of-scope work is agreed by email and never makes it into the fee schedule.
• Renewals are not prompted, so a three-year-old letter is the only signed scope on file.

What SpidNums does not do

SpidNums is practice management with an invoicing workflow, not an accounts-receivable ledger. It produces the priced, signed engagement that your billing runs from — it does not process payments or age receivables.

If your firm already runs a tracking system it trusts, the honest answer is that you do not need this one. The pages on this site are written to help you decide, not to pretend every firm has the same problem.