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The notion of doubling time dates to interest on loans in Babylonian mathematics. Clay tablets from circa 2000 BCE include the exercise "Given an interest rate of 1/60 per month (no compounding), come the doubling time." This yields an annual interest rate of 12/60 = 20%, and hence a doubling time of 100% growth/20% growth per year = 5 years.
The doubling time (t d) of a population is the time required for the population to grow to twice its size. [24] We can calculate the doubling time of a geometric population using the equation: N t = λ t N 0 by exploiting our knowledge of the fact that the population (N) is twice its size (2N) after the doubling time. [20]
Rank Country (or dependent territory) July 1, 2015 projection [1] % of pop. Average relative annual growth (%) [2] Average absolute annual growth [3]Estimated doubling time
The formula above can be used for more than calculating the doubling time. If one wants to know the tripling time, for example, replace the constant 2 in the numerator with 3. As another example, if one wants to know the number of periods it takes for the initial value to rise by 50%, replace the constant 2 with 1.5.
A popular approximated method for calculating the doubling time from the growth rate is the rule of 70, that is, /. Graphs comparing doubling times and half lives of exponential growths (bold lines) and decay (faint lines), and their 70/ t and 72/ t approximations.
Population growth is the increase in the number of people in a population or dispersed group. The global population has grown from 1 billion in 1800 to 8.2 billion in 2025. [ 2 ] Actual global human population growth amounts to around 70 million annually, or 0.85% per year.
For example, in microbiology, a population of cells undergoing exponential growth by mitosis replaces each cell by two daughter cells, so that = and is the population doubling time. If the population grows with exponential growth rate r {\displaystyle \textstyle r} , so the population size at time t {\displaystyle t} is given by
To the right of each year column (except for the initial 1950 one), a percentage figure is shown, which gives the average annual growth for the previous five-year period. Thus, the figures after the 1960 column show the percentage annual growth for the 1955-60 period; the figures after the 1980 column calculate the same value for 1975–80; and ...