If you sell goods or services in Quebec, you already know the tax math can get confusing fast. Two separate taxes, two separate rates, and a calculation method that trips up even experienced bookkeepers. Getting it wrong means over-charging customers or under-remitting to Revenu Québec, and neither ends well. This guide walks you through exactly how a GST QST calculator works, step by step. You'll learn what each tax is, the current rates, the precise formulas, and how to apply them with real-dollar examples. By the end, you'll be able to calculate Quebec sales taxes confidently, whether you run a corner café in Montréal or an online store shipping into the province.