What is compound interest?

Compound interest is interest calculated on both the initial principal and the accumulated interest from previous periods. This means your interest earns interest, creating exponential growth over time. It contrasts with simple interest, which is only calculated on the principal.

How does compounding frequency affect returns?

More frequent compounding leads to higher returns. For example, $10,000 at 8% for 10 years: annually gives $21,589; monthly gives $22,196; daily gives $22,253. The difference grows larger with higher rates and longer time periods.

What is the Rule of 72?

The Rule of 72 is a quick mental math shortcut to estimate how long it takes for an investment to double. Simply divide 72 by the annual interest rate. At 8% per year, money doubles in approximately 72 ÷ 8 = 9 years.

What is the effective annual rate (EAR)?

The effective annual rate accounts for compounding within the year, giving the true annual return. A 12% rate compounded monthly has an EAR of (1 + 0.12/12)^12 − 1 ≈ 12.68%. The EAR is always higher than the nominal rate when compounding occurs more than once per year.

How is compound interest different from simple interest?

Simple interest: I = P × r × t. Compound interest: A = P × (1 + r/n)^(nt). For $1,000 at 10% for 5 years: simple interest gives $1,500; compound interest (annual) gives $1,610.51. The gap widens dramatically over longer periods.

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Compound Interest Calculator

Calculate compound interest, final amount, and total interest earned with different compounding frequencies. See the power of compounding.

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A = P × (1 + r/n)^(n×t)

Variables

AFinal amount

PPrincipal (initial amount)

rAnnual interest rate (decimal)

nCompounding frequency per year

tTime in years

Explanation

Compound interest is interest calculated on both the initial principal and the accumulated interest from previous periods. Unlike simple interest (which only earns on the principal), compound interest grows exponentially - this is why Einstein allegedly called it 'the eighth wonder of the world'.

What is the Compound Interest Calculator?

Compound interest is one of the most powerful forces in personal finance and investing. Often described as 'interest on interest,' it causes wealth to grow exponentially rather than linearly. Understanding compound interest is fundamental to making informed decisions about savings accounts, investments, loans, and retirement planning.

How to Use This Calculator

Enter your principal amount, annual interest rate, time period, and compounding frequency. The calculator instantly shows your final amount, total interest earned, effective annual rate, and estimated doubling time using the Rule of 72.

Why Use MyCalculatorsHub's Compound Interest Calculator?

This calculator helps you visualize the long-term impact of different interest rates and compounding frequencies, making it invaluable for comparing investment options, planning retirement savings, and understanding the true cost of loans.

Common Mistakes to Avoid

A common mistake is confusing the nominal rate with the effective annual rate. When comparing financial products, always compare effective rates. Also, remember that higher compounding frequency (daily vs. annual) does increase returns, but the difference is often smaller than expected.