Simple Interest vs Compound Interest
Interest is the cost of borrowing money or the reward for saving it. There are two fundamental ways interest is calculated: simple interest and compound interest. Understanding the difference is essential for making informed financial decisions, whether you are taking a loan or growing your investments.
Simple interest is calculated only on the original principal amount. The interest earned each year remains constant. The formula is: Interest = P × R × T, where P is the principal, R is the rate, and T is the time in years.
Compound interest is calculated on the principal plus the accumulated interest from previous periods. This "interest on interest" effect causes exponential growth over time. The formula is: A = P × (1 + r/n)^(n×t), where n is the compounding frequency per year.
Compounding frequency matters
How often interest compounds has a direct impact on your total returns. The more frequently interest is compounded, the higher the effective annual rate:
At a nominal rate of 12%, yearly compounding gives an effective rate of 12.00%, monthly compounding gives 12.68%, and daily compounding gives approximately 12.75%. For long-term investments, this difference compounds significantly over decades.
When to use simple vs compound interest
Simple interest is typically used for short-term loans, some bonds, and certain consumer finance products. Compound interest applies to most savings accounts, fixed deposits (with periodic payouts reinvested), mutual funds, stocks, and retirement accounts. Always check whether your investment or loan uses simple or compound interest — it can make a substantial difference in the total amount earned or owed.