The Compound Interest Calculator shows how your investments grow over time when interest earns interest. Unlike simple interest (calculated only on the original principal), compound interest is calculated on both the initial principal and the accumulated interest from previous periods — creating exponential growth often called 'the eighth wonder of the world.'
Albert Einstein reportedly called compound interest 'the most powerful force in the universe.' Whether or not he actually said it, the math is undeniable. Starting with $10,000 and earning 7% annually, you'd have $19,672 after 10 years, $38,697 after 20 years, and $76,123 after 30 years — without adding a single dollar. The longer your money compounds, the faster it grows.
Compound interest works both ways. On savings and investments, it's your best friend. On debt (credit cards, loans), it's your worst enemy. A $5,000 credit card balance at 22% APR, with only minimum payments, can take over 20 years to pay off and cost more than $10,000 in interest.
How the Formula Works
A = P(1 + r/n)^(nt), where A = final amount, P = principal, r = annual interest rate (decimal), n = compounding frequency per year, t = time in years.
P = Initial principal (starting amount)
r = Annual interest rate as a decimal (e.g., 7% = 0.07)
n = Number of times interest compounds per year (12 = monthly, 4 = quarterly, 1 = annually)
t = Number of years
Interest earned = A − P
With regular contributions: A = P(1 + r/n)^(nt) + PMT × [((1 + r/n)^(nt) − 1) ÷ (r/n)]
How to Use This Calculator
Enter your initial investment (principal) amount
Enter the annual interest rate
Select the compounding frequency (daily, monthly, quarterly, or annually)
Enter the investment time period in years
Optionally add regular monthly or annual contributions
View the growth chart and final amount
Tips & Best Practices
Start investing as early as possible — time is your greatest asset with compound interest
Choose investments with more frequent compounding when possible
Reinvest dividends and interest rather than withdrawing them
Consistent small contributions add up enormously over decades
Use the Rule of 72 to quickly estimate doubling time
Important Limitations
Assumes a constant rate of return — real investment returns vary year to year
Does not account for inflation, taxes on gains, or investment fees
Past returns do not guarantee future performance
Does not factor in the risk associated with different types of investments