Why tipping customs vary
Tipping expectations differ because of varying wage structures, cultural norms, and whether service charges are included in prices. In the US, servers rely on tips as a major income source, making 15 to 20 percent standard. In Japan, tipping can be considered rude. Most European countries include service in the price but rounding up is common.
Not knowing local customs can lead to undertipping (appearing rude) or overtipping (wasting money or creating awkward situations). A quick lookup before dining saves both.