When does your cd4 start to decrease if hiv?

Varies: This is difficult to predict. In most individuals there is a gradual fall in CD4 counts from onset of disease over about an 8-12 year course until it becomes so low that the immune deficiencies manifest in susceptibility to opportunist pathogens (organisms which would otherwise not produce disease in normal humans). In some people the disease may progress for 20+ yrs very slowly.