Average adult size is 3-4 inches, but can reach 5 inches. They can live 10-15 years. Juvenile littleneck clams are 0.26-0.28 mm in shell length at settlement. They usually mature sexually after 1.5 years, at 15-35 mm shell length. Littlenecks may live 13-16 year to a maximum size of 80 mm.
Growth rates vary widely, depending upon substrate, clam densities, tidal level, and location.
Growth rates can be slower in exposed areas and faster in protected sites. Their average size at the end of the second year is 25 mm and 35 mm at the end of the third year. Growth rates and shape of the shell of softshell clams are dependent on the substrate. Softshells may reach maturity at one year of age and 27-34 mm shell length. They have been reported to live up to 28 years, but 10-12 years is more likely the maximum age.