Canada has a North American tipping culture, but the cleanest base is the pre-tax subtotal. Tourism authorities commonly describe 15% to 20% as standard for good sit-down restaurant service. The terminal's biggest button is a suggestion, not a mathematical law.
Three numbers can all say eighteen percent
Find the quiet line above the tax
Post-tax percentages wear a larger coat
An 18% tip on the C$90.40 post-tax amount would be C$16.27, which is just over 20% of the C$80 meal. That may be exactly what you want to give, but it should be your generosity rather than a surprise hidden inside the terminal's calculation base.
Check for the group gratuity first
Restaurants may add an automatic gratuity for larger parties. Destination Toronto advises checking the bill before adding a tip. If a service or gratuity line is already present, do not tip the same service twice unless you deliberately want to add more.
The counter screen is not a referendum
Coffee shops, bakeries and take-away counters may rotate a tip screen toward you. Select zero, a small amount or a percentage based on the service you received. The presence of buttons does not create a new national rule.
Keep direct thanks simple
For a taxi, haircut or other personal service, 15% to 20% is a familiar range. For a guide, porter or hotel worker, a direct Canadian-dollar amount is often easier to understand than importing the restaurant percentage. In every setting, warm service and local context matter more than performing arithmetic for its own sake.