Compound Interest Calculator
See how compounding grows your money over time with customizable frequencies.
Compound Interest & Growth Calculator
Calculate exponential wealth accumulation across annual, quarterly, or monthly compounding.
How Compound Interest Works
Unlike simple interest—which generates interest exclusively on the original principal deposit—compound interest is calculated on both the initial principal and the accumulated interest from preceding periods. Often termed "interest on interest", compounding accelerates financial growth exponentially over time.
The Universal Compound Interest Formula
The mathematical formula for calculating compound interest maturity is:
A = P × [1 + (r ÷ n)]^(n × t)
• A = Final accumulated amount (Principal + Interest)
• P = Initial principal balance (e.g. $10,000)
• r = Annual nominal interest rate expressed as a decimal (8% = 0.08)
• n = Compounding frequency per year (1 for annual, 4 for quarterly, 12 for monthly)
• t = Number of elapsed years (e.g. 5)
Worked Real-World Compounding Example
Standard retail bank savings certificates typically compound on a quarterly basis (n = 4). Let's evaluate $10,000 invested at 8% per annum for 5 years:
- Principal: $10,000
- Quarterly Rate: 0.08 ÷ 4 = 0.02 (2% per quarter)
- Total Quarters: 5 × 4 = 20 quarters
- Calculation: $10,000 × (1.02)^20 = $10,000 × 1.485947 = $14,859.47
- Interest Earned: $4,859.47 (Compared to $4,000 under simple interest)
The Handy "Rule of 72"
The Rule of 72 provides a mental shortcut for estimating how many years it will take to double your money at a fixed compound rate:
For instance, at an 8% return, your money doubles in approximately 72 ÷ 8 = 9 years. At 12%, doubling takes only 72 ÷ 12 = 6 years.