Chikungunya virus (CHIKV) and Zika virus (ZIKV) are arthropod-borne viruses transmitted mainly by mosquitoes. These viruses have become endemic in large parts of North, Central, and South America. Arboviruses persistently infect mosquitoes throughout their life span and become infectious (i.e., expectorate infectious virus in saliva) after a period of time called the extrinsic incubation period (EIP). The duration of this infectiousness, however, is not well characterized. This is an important shortcoming because many epidemiological models assume that mosquitoes continue to be infectious for the duration of their life span. To define the duration of infectiousness for CHIKV and ZIKV, mosquitoes were infected orally with these viruses. Every 2 days, legs/wings, midguts, salivary glands, and saliva were collected from 30 to 60 mosquitoes and viral load measured. In CHIKV-infected mosquitoes, infectious virus in saliva peaked early (2-4 dpi), and then decreased rapidly and was rarely observed after 10 dpi. Viral RNA in infected tissues also decreased after the initial peak (4-8 dpi) but did so much less drastically. In ZIKV-infected mosquitoes, the infectious virus in saliva peaked at 12-14 dpi and dropped off only slightly after 14 dpi. In infected tissues, viral RNA increased early during infection, and then plateaued after 6-10 days. Our findings suggest that significant variation exists in the duration of the infectious period for arboviruses that is in part influenced by virus clearance from expectorated saliva.