Treat country presets as starting assumptions, then inspect the actual bill.
Use the Tipping Calculator by Country alongside this illustrative example.
A practical example
On a bill of 50, choosing an illustrative 10% additional gratuity adds 5. If the printed bill already contains a service charge, first decide whether any additional tip is intended; applying a preset without reading the bill can add an amount you did not mean to pay.
Check the result
Ask how the charge is described and whether it is included, optional or separate. Customs can differ between a restaurant, a hotel and a tour even within one country.
Try a comparison
Compare zero additional gratuity with your chosen percentage after reading the service charge. The difference is the extra amount you are deciding to add, not necessarily the total service payment already in the bill. Keep that distinction visible when explaining a shared total.
What this does not establish
A country label is not a legal obligation or a universal etiquette rule. Use local context and your own choice rather than treating the default as mandatory.