Compound Interest
The principle by which the interest you earn also earns interest over time, leading to exponential growth of investments.
Compound interest is the eighth wonder of the world. It is the mathematical concept where the interest you earn on an initial investment (the principal) begins to earn interest itself in subsequent periods.
Unlike simple interest, which is calculated only on the principal amount, compound interest causes wealth to grow exponentially over long time horizons.
The Mathematical Formula
The standard formula for compound interest is:
A = P(1 + r/n)^(nt)
Where:
- A = the future value of the investment/loan, including interest
- P = the principal investment amount
- r = the annual interest rate (decimal)
- n = the number of times that interest is compounded per unit t
- t = the time the money is invested or borrowed for
Real-World Application
Compound interest is the foundation of modern retirement planning, Systematic Investment Plans (SIPs), and long-term stock market investing. By starting early and allowing decades for the compounding effect to take place, even small monthly contributions can grow into massive portfolios.
Conversely, compound interest works against you when carrying high-interest debt, such as credit card balances, causing the total amount owed to skyrocket if only minimum payments are made.