Three phases of growth in a typical sigmoidal curve.

A sigmoidal curve (solid black line) typically includes an initial exponential phase, an approximately linear phase (which contains the inflection point at which the growth rate is maximal) and finally an asymptotic phase, in which the curve approaches a constant asymptote as . In some cases, the initial exponential phase is so short as to be imperceptible, but the linear and asymptotic regions are features of all sigmoidal curves. Attenuating curves are similar but lack the initial exponential phase, much like a sigmoidal curve that starts with its inflection point at .