Austin, Texas added roughly 170 newcomers a day during its 2010s boom — and growth like that compounds, because each year's newcomers have children and attract more newcomers. The classic model is exponential: P = P₀ × e^(rt), where P₀ is the starting population, r is the annual growth rate as a decimal, t is years, and e is Euler's number (~2.71828). At 2% annual growth, a town of 50,000 reaches about 61,000 in a decade — and the Rule of 70 says any population growing at r percent doubles in roughly 70 ÷ r years, so 2% growth doubles in about 35 years.

City planners size schools and sewers from these curves, epidemiologists model outbreaks, and ecologists track invasive species — though all of them know exponential growth eventually hits limits (food, space, immunity), which is where the S-shaped logistic model takes over. This calculator evaluates the growth factor e^(rt): compute e^(rt) on paper — for r = 0.02 and t = 10, e^0.2 ≈ 1.2214 — type your starting population in the Variable A box (50000), and type the growth factor in the Variable B box (1.2214). The Result box shows about 61,070, the projected population. Compare scenarios by changing B: r = 3% for 10 years gives e^0.3 ≈ 1.3499 and a town of 67,495.

With the pre-filled defaults — Variable A 10, Variable B 5 — the Population Growth Calculator returns Result 50.0000. Change any input and those results update instantly, so you can see exactly how each number you enter moves the answer.