Population Growth Rate Calculator
Enter a starting and ending population along with the number of years between them to estimate the annual growth rate and how long it would take the population to double.
What Is Population Growth Rate?
Population growth rate measures how fast a population of people, animals, or any organism is increasing (or decreasing) over time, expressed as a percentage per year. Ecologists and demographers use it to track species recovery, invasive species spread, or human community trends.
The Formula
This calculator uses the standard compound (exponential) growth formula: r = [(Pt / P0)^(1/t) − 1] × 100, where P0 is the initial population, Pt is the population after time t (in years), and r is the annual growth rate. Doubling time is estimated with the well-known Rule of 70: doubling time ≈ 70 / r.
How to Use the Result
A positive growth rate means the population is expanding; a negative rate means it is declining. The doubling time gives a quick sense of how fast growth is compounding if the rate stays constant, which is a simplification — real populations are affected by resource limits, predation, migration, and other factors not captured by this basic exponential model.
- For general educational and planning purposes only.
- Real-world population dynamics are rarely perfectly exponential over long periods.