QST/TVQ registration validator.

How the QST/TVQ number is structured

Revenu Québec's own "Application Programming Interface (API) Used to Validate a QST Registration Number" and "Validation of a QST Registration Number" pages both describe the required input as "the registration number (ten digits followed by the letters TQ and four more digits)" — 16 characters in total. The validation-service page gives a worked example: 9999999999 TQ 0001. This mirrors the shape of the federal Business Number (9-digit root + 2-letter program code + 4-digit reference), but Quebec's root is 10 digits and the program code is always the fixed letters "TQ" (the law under which the tax is collected), not a variable 2-letter code like the federal "RT".

The 9-digit exception

Both Revenu Québec pages document one real exception: if a QST registration number is only 9 digits, carries no "TQ", and is identical to the business's federal GST/HST number, the business is a selected listed financial institution. Revenu Québec has mandated the Canada Revenue Agency to administer the QST such businesses collect, so that number should be checked against the federal GST/HST Registry instead of Revenu Québec's own tool.

No checksum exists on the QST number itself

Just like the CRA Business Number, Revenu Québec has never published a check-digit algorithm for the QST registration number. Its own validation pages confirm a number by querying Revenu Québec's live registry — returning registration status, effective date and business name — not by a public formula. That means this tool can tell you a QST number is the right shape, but it cannot tell you whether a specific number was ever actually issued to a real business; only Revenu Québec's own validation service or API can do that.