The exponential growth and arithmetic growth can be respectively expressed as

 The exponential growth can be expressed as W ₁ = W ^₀ e ^rt 

W ₁ = final size (weight, height, number etc.) W ^₀ = initial size at the beginning of the period r = growth rate t = time of growth e = base of natural logarithms.

Arithmetic growth rate is expressed mathematically, as L _t = L ₀ + rt

 L _t = length at time ‘t’ L ₀ = length at time ‘zero’ r = growth rate / elongation per unit time