Some policies require you to pay a fixed amount, for instance $40 for massage, rather than a percentage of you total amount. A good extra is the one that meets you half way. So as not to lose out, go for extras that cover 60 to 100% of your bill. Insurance extras that charge a percentage rather than a fixed amount are quite useful when visiting practices that charge above the average price. When you come across extras, always compare different providers and see who provides a higher limit per year.