HST Net Tax Explained: How Ontario Businesses Calculate What They Owe

Every registered Ontario business that charges HST eventually has to answer one question at filing time: does the business owe the CRA money, or does the CRA owe the business money? The answer comes from a single calculation — the HST net tax calculation — and understanding it removes a lot of the mystery from what otherwise looks like a confusing government form.

At its core, the math is simple: HST collected from customers minus HST paid on eligible business purchases. But a few wrinkles — what counts as "collected," which purchases actually qualify, and how the filing period affects the numbers — trip up a lot of business owners, especially in their first year of registration.

This guide walks through the formula, a worked example, and what to do once you know whether you owe or are owed.

The Basic Formula

Two components combine to produce net tax:

Net tax = HST collected − ITCs claimed.

If the result is positive, you owe that amount to the CRA. If it's negative, the CRA owes you a refund.

Why "Collectible" Matters, Not Just "Collected"

One detail that surprises new registrants: the calculation generally runs on amounts that became collectible during the period — meaning HST you invoiced, even on unpaid invoices — not strictly cash actually received into the bank account. Confirm which basis applies under your specific filing method before relying on your bookkeeping software's default report.

A Worked Example (Illustrative Only — Use Your Actual Numbers)

Say an Ontario consulting business invoices $20,000 in fees over a reporting period. At the HST rate for Ontario — 13%, as of mid-2026, always verify the current rate before filing — that works out to $2,600 in HST collected.

During the same period, the business pays $4,000 in eligible expenses, generating $520 in HST paid that qualifies as an input tax credit.

Net tax = $2,600 − $520 = $2,080 owing.

If that same business had a slow sales quarter but a large one-time equipment purchase, the input-tax-credit side could exceed the collected side, producing a negative net tax — a refund situation, which we cover in a companion article on HST refunds.

Filing Frequency and Reporting Periods

The CRA assigns — or, within limits, lets you elect — a reporting period, generally monthly, quarterly, or annually depending on your business's revenue. Whatever period applies, the net tax calculation is done fresh for that period; a bad quarter doesn't automatically offset a good one until the next return is filed.

Common Mistakes in the Calculation

• Forgetting exempt or zero-rated sales. Not everything you sell necessarily carries HST; exempt and zero-rated supplies need to be tracked separately from taxable ones.
• Claiming ITCs without adequate documentation. An expense you paid HST on doesn't become a valid credit without records that meet CRA requirements.
• Mixing personal and business expenses. Only the business-use portion of a mixed expense supports an input tax credit.
• Missing the reporting-period cut-off. Sales invoiced right at period-end can land in the wrong return if your books aren't reconciled to the correct date.

Frequently asked questions