You would think that when a business starts would be obvious, but that’s not always the case. You might think that a business starts when it first opens its doors, but that’s not a very good definition because of all the things that had to happen before that happened – some of which you’ll want to claim as business expenses.
A better definition of when a business starts comes from the Canada Revenue Agency. In their Business and Professional Income Guide, they state that they generally consider that a business starts "whenever you start some significant activity that is a regular part of the business, or that is necessary to get the business going".
So in practice, a business starts when the activities related to the business’s operation start. If I start a tailoring business, for example, my business starts when I buy the supplies I need rather than when I alter that first customer’s garment.
