A quantity growth model in which the rate of growth is directly proportional to the amount present. Exponential growth is often expressed as A = A₀b^t (where b > 1 ) or A = A₀e^kt (where k is a positive number representing the rate of growth). In both formulas A₀ is the original amount present at time t = 0.

Exponential growth is often used for such phenomena as inflation or population growth. For example, A = 3000e^0.05t is a model for the exponential growth of $3000 invested at 5% gain per year compounded continuously.