Compound interest is the addition of interest to the principal sum of a loan or deposit, or in other terms, interest on interest. It is the result of reinvesting interest, rather than paying it out, so that interest in the next period is then earned on the principal sum plus previously accumulated interest. This cumulative loop generates an exponential growth curve, which is the foundational mathematical basis behind long-term wealth growth and retirement asset compounding.
In-Content Ad Slot - Financial & Investment Targets
The standard algebraic formula for calculating compound interest with periodic contributions is structured as follows:
Compounding frequency determines how often the interest is calculated and added back to the investment balance. The more frequently interest is calculated (daily vs annually), the faster your balance compounds. Let's look at how a $10,000 principal at a 10% annual rate behaves across various frequencies over 1 year:
The Rule of 72 is a quick, useful shorthand tool to estimate the number of years required to double your starting investment at a fixed interest rate. To find the years to double, divide 72 by your annual rate of return: Years to Double = 72 / Interest Rate. For instance, at an 8% interest rate, your money will double approximately every 9 years (72 / 8 = 9). This simple metric aligns perfectly with our interactive visual charts.