Free Compound Interest Calculator
See the power of compound interest - "the eighth wonder of the world." Calculate how your investments grow exponentially over time.
The Rule of 72
Quick way to estimate how long it takes to double your money:
Frequently Asked Questions About Compound Interest
Compound interest is 'interest on interest' – you earn returns not just on your initial investment, but also on accumulated interest. Unlike simple interest (calculated only on principal), compound interest grows exponentially. For example, $1,000 at 5% annual compound interest becomes $1,050 after year 1, then $1,102.50 after year 2 (5% on $1,050).
The compound interest formula is: A = P(1 + r/n)^(nt), where A = final amount, P = principal (initial investment), r = annual interest rate (decimal), n = number of times interest compounds per year, t = number of years. For continuous compounding: A = Pe^(rt).
More frequent compounding results in higher returns. Compounding options include: annually (1x/year), semi-annually (2x), quarterly (4x), monthly (12x), daily (365x), or continuously. The difference is most significant at higher interest rates and longer time periods. Monthly compounding is common for savings accounts.
The Rule of 72 is a quick way to estimate how long it takes to double your money. Divide 72 by the interest rate to get the years to double. For example, at 8% interest, money doubles in about 72 ÷ 8 = 9 years. At 6%, it takes 72 ÷ 6 = 12 years.
Regular contributions dramatically accelerate compound growth. Adding monthly or yearly deposits creates multiple 'money engines' each earning compound interest. For example, $100/month invested at 7% for 30 years totals $36,000 in contributions but grows to over $121,000 due to compound interest.
Understanding Compound Interest
Albert Einstein reportedly called compound interest "the eighth wonder of the world," adding that "he who understands it, earns it; he who doesn't, pays it." Whether or not Einstein actually said this, the principle holds true: compound interest is one of the most powerful forces in personal finance.
Unlike simple interest, which is calculated only on the principal amount, compound interest is calculated on both the initial principal and the accumulated interest from previous periods. This creates an exponential growth curve, where your money grows faster and faster over time.
Our compound interest calculator helps you visualize this growth by showing year-by-year projections. You can experiment with different principal amounts, interest rates, compounding frequencies, and time periods to see how each factor affects your final balance.
The key to maximizing compound interest is time. The earlier you start investing, the more time your money has to compound. Even small regular contributions can grow to substantial sums over decades, making early and consistent investing one of the best strategies for building long-term wealth.