How serious is haemophilia?

The severity of haemophilia is determined by the level of clotting activity of factor VIII or factor IX in the blood. There are three levels of severity: mild, moderate, and severe. The following table shows the range of factor VIII and factor IX activity:
People with severe haemophilia usually bleed frequently into their muscles or joints. They may bleed one to two times per week. Bleeding is often spontaneous, which means the bleeding just happens with no obvious cause.

People with moderate haemophilia bleed less frequently, usually after an injury, perhaps once a month. Cases of haemophilia vary, however, and a person with moderate haemophilia can bleed spontaneously.

People with mild haemophilia usually bleed only as a result of surgery or major injury. They may never have a bleeding problem.