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Population Growth Rate Calculator

Biology

Calculate exponential population growth using N(t) = N0 × e^(rt). Enter initial population, growth rate, and time for ecology and biology projections.

110,000,000,000
-50100
01,000

Final Population

1,648.72
Population Change
648.72
Percent Change
64.87%

This calculator computes your Final Population, Population Change, Percent Change from the values you enter.

Inputs
Initial Population (N₀)Growth Rate (r)Time Elapsed
Outputs
Final PopulationPopulation ChangePercent Change

What is a Population Growth?

The Population Growth Rate Calculator projects future population size using the exponential growth model N(t) = N₀ × e^(rt). Enter the initial population, a growth rate, and the elapsed time, and the calculator instantly returns the final population, the total increase, and the percentage change.

This model is a foundational tool in ecology, microbiology, and demographics for projecting growth when resources are effectively unlimited. For the related question of how long it takes a population to double, see the Bacterial Doubling Time Calculator.

How to use this Population Growth calculator

  1. Enter the initial population (N₀) — the starting number of individuals.

  2. Enter the growth rate (r) — as a percentage per time period (can be negative for a declining population).

  3. Enter the elapsed time — the number of periods over which growth occurs, using the same time unit as your growth rate.

  4. Read the final population result — the highlighted result shows the projected population after the given time, with the absolute and percentage change shown alongside.

Formula & Methodology

Exponential growth formula:
N(t) = N₀ × e^(rt)

Variable definitions:
- N₀ — initial population
- r — growth rate per time period (as a decimal in the formula; entered as a percentage in the calculator)
- t — elapsed time (number of periods)
- e — Euler's number, approximately 2.71828
- N(t) — final population after time t

Worked example:

An initial population of 1,000 with a 5% growth rate over 10 periods:

N(10) = 1,000 × e^(0.05 × 10) = 1,000 × e^0.5 ≈ 1,648.7

Note: This calculator models unconstrained exponential growth, which doesn't account for resource limits, competition, or carrying capacity. Real populations typically follow logistic growth, slowing as they approach environmental limits — this model is most accurate for short time horizons or resource-unlimited scenarios.

Frequently Asked Questions

Exponential population growth is calculated as N(t) = N₀ × e^(rt), where N₀ is the initial population, r is the growth rate (as a decimal), t is the elapsed time, and e is Euler's number (≈2.71828). This calculator applies that formula directly using the population, rate, and time you enter.
The growth rate r represents the net per-capita rate of population change per unit time — the birth rate minus the death rate (and, in ecology, sometimes adjusted for migration), expressed as a percentage in this calculator. A positive r means the population is growing; a negative r means it's declining.
Linear growth adds a fixed amount each period, while exponential growth compounds — the growth amount itself increases as the population grows, since growth is proportional to the current population size. This is why populations under sustained exponential growth can increase dramatically over time, even from modest growth rates.
No — this calculator models unconstrained exponential growth (the exponential/Malthusian growth model), which assumes unlimited resources and no environmental limits. Real populations eventually slow as they approach a carrying capacity, a pattern better described by logistic growth models, which this simpler exponential formula doesn't capture.
Yes — entering a negative growth rate models a declining population (like an endangered species or a population facing high mortality), and the formula works the same way, producing a final population smaller than the initial population as time increases.
Mathematically, continuous exponential population growth (N₀e^rt) and continuously compounded interest use the identical formula structure, just applied to different quantities — population size instead of money. The underlying compounding logic (growth proportional to current size) is the same in both cases.
Bacterial colonies growing in ideal lab conditions, invasive species colonizing a new habitat with abundant resources, and early-stage human population growth in regions with high birth rates and low mortality are all commonly modeled with exponential growth, at least until resource limits or other factors slow the rate.
The growth rate and time period must use consistent units — if your growth rate is an annual rate (like "5% per year"), then time must also be measured in years for the formula to produce a correct result. Mixing units (e.g., an annual rate with a time in months) will give an incorrect final population.
Bacterial doubling time and this exponential growth model both use the same underlying N(t) = N₀e^(rt) equation — doubling time is simply the specific time it takes for a population to double, computed as ln(2) ÷ r. See the [Bacterial Doubling Time Calculator](/bacterial-doubling-time-calculator/) to calculate doubling time directly.
Ecologists use exponential growth models to estimate short-term population trajectories for species without significant resource constraints (like early recovery-phase endangered species populations), to project invasive species spread, and to compare theoretical unconstrained growth against observed real-world growth to detect environmental limiting factors.
Percent change expresses the population increase (or decrease) relative to the starting population, making it easy to compare growth impact across populations of very different starting sizes — a 50% increase means the same relative growth whether the starting population was 100 or 1,000,000.
Using e models continuous, uninterrupted growth (compounding at every instant) rather than growth applied only at fixed intervals (like once per year). This continuous model is the standard mathematical idealization used in ecology, epidemiology, and finance whenever growth is assumed to happen constantly rather than in discrete steps.
Also known as
exponential growth calculatorN = N0e^rt calculatorecology population calculatorspecies growth calculator