Tipping is not common in Belgium. Restaurant, taxi and hairdresser bills include the service charge. Service staff in Belgium are well-paid, in comparsion with those in the USA, and do not rely on tips to make up their income.

However, if you are very happy with the service you got, leaving a few Euros (or to round up your bill) as a tip is the way forward, but think of 10% as the maximum to leave (i.e. when you receive exceptional service).

In some of the touristy places in Brussels, you may find that the staff 'expect' you to tip more. You are under no obligation and are well-advised to stick to your guns.