Do I owe HST if I convert my commercial building to a different use than when I bought it?

It depends on the specific change, but converting a commercial property to a different use can trigger an HST self-assessment obligation under the Excise Tax Act's change-of-use rules. Broadly, if you originally used the property in a way that let you claim input tax credits, for example, in a fully taxable commercial activity, and you later shift its use toward something that wouldn't have qualified for those credits, such as exempt residential use, the change itself can be treated as a taxable event, requiring you to self-assess HST on the property's value at that point.

The reverse can also happen: converting a property from a use that didn't generate input tax credits to one that does can allow you to claim credits going forward, or trigger different consequences depending on the type of change and how much of the property is affected. Partial changes in use, converting only part of a building, add another layer of complexity, since the tax treatment can apply proportionally rather than to the whole property.

Because the specific facts of the conversion drive the result, this needs a proper HST change-of-use analysis from an advisor before or as soon as the conversion happens, not after the fact.