Exponential Growth & Decay Calculator

This calculator models exponential growth and decay, working out how a quantity changes over time when it grows or shrinks by a fixed percentage each period. Exponential change is one of the most important patterns in nature, finance and science, because so many things grow or decay in proportion to their current size: money earning compound interest, populations of people, animals or bacteria, the spread of information, and the decay of radioactive material or a drug in the bloodstream. Unlike linear change, which adds the same amount each step, exponential change multiplies by the same factor each step, which is why it starts slowly and then accelerates dramatically, or, for decay, falls quickly at first and then tails off. This tool captures both. You enter the starting value, the percentage rate per period, positive for growth or negative for decay, and the number of periods, and the calculator returns the final value, the total change, the growth or decay factor, and the doubling time for growth or half-life for decay, the time it takes for the quantity to double or halve. The results update as you type, so you can explore how even a modest rate compounds into a large change over many periods. Use it for finance and investment projections, population and biology problems, radioactive decay, or any situation that compounds. The doubling time and half-life are especially useful intuitions: a quantity growing at a steady rate always takes the same time to double again, no matter how large it has become, which is the surprising power of exponential growth. The calculation uses the standard compound formula and is rounded for display.

Final = start x (1 + rate/100)^periods. Positive rate grows; negative rate decays. Doubling time (growth) or half-life (decay) is shown. Rounded for display.