Compound Interest Calculator

Project Investment Growth

See how an initial principal grows from compounding. This tool does not include recurring contributions.

Growth summary

Future value Enter investment details Starting value, growth, and final value will appear here.

Assumes a fixed annual rate and no additional contributions, withdrawals, fees, taxes, or inflation.

Important Finance Disclaimer

This calculator is for estimates only and educational purposes. It does not constitute financial, investment, loan, tax, legal, accounting, or other professional advice. Always verify important decisions with a qualified professional and the relevant lender, advisor, tax authority, or service provider.

Inputs, units, and periods

  • Currency inputs are treated as nominal dollar amounts.
  • The interest rate is the nominal annual rate entered as a percent.
  • The time period is measured in years.
  • The selected compounding frequency is applied as periods per year.

Items not included

  • Taxes, investment fees, account charges, withdrawal penalties, and inflation.
  • Market volatility, changing rates, dividend timing, and irregular contributions.
  • Broker, bank, or platform rules that change how interest is credited.

Actual outcomes can differ because of rounding, fees, taxes, insurance, compounding rules, APR disclosures, loan terms, market conditions, provider policies, and the exact timing of payments or cash flows.

What is Compound Interest?

Compound interest is interest calculated on both the initial principal and the accumulated interest from previous periods. Unlike simple interest, compound interest allows your money to grow faster because you earn interest on your interest.

This powerful concept is the foundation of long-term investing and wealth building. It's often called the "eighth wonder of the world" because of its dramatic effect on growing investments over time.

How Compound Interest Is Calculated

Follow these detailed steps:

  1. Step 1: Identify Your Variables
    Gather your principal (P), annual interest rate (r), time period (t), and compounding frequency (n). Each variable significantly impacts your final result.
  2. Step 2: Apply the Compound Formula
    Use A = P(1 + r/n)^(nt). For $10,000 at 5% compounded monthly for 10 years: A = 10000(1 + 0.05/12)^(12x10) = $16,470.09.
  3. Step 3: Calculate Interest Earned
    Subtract principal from final amount: Interest = A - P. In our example: $16,470.09 - $10,000 = $6,470.09 earned.

Formula

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

Example

Investment Growth Example

Problem: You invest $10,000 at 5% annual interest, compounded monthly for 10 years. How much will you have?

Solution:

  1. Principal: $10,000, Rate: 5% (0.05), Time: 10 years, n = 12
  2. Formula: A = 10,000 × (1 + 0.05/12)^(12×10)
  3. Result: A = $16,470.09
  4. Interest earned: $16,470.09 - $10,000 = $6,470.09

Quick Calculation Tips

  • More frequent compounding = higher returns (daily > monthly > annually)
  • The Rule of 72: Divide 72 by your interest rate to estimate doubling time
  • Start early - time is your biggest ally in compound growth
  • Reinvest dividends to maximize compound effect

Common Mistakes to Avoid

  • Ignoring compounding frequency
    Daily compounding can add 0.1-0.3% more return annually vs annual compounding at the same rate.
  • Forgetting to account for inflation
    Real returns = nominal returns - inflation rate. 5% returns with 3% inflation = 2% real return.

Frequently Asked Questions

What's the difference between compound and simple interest?

Simple interest is calculated only on the principal amount. Compound interest is calculated on the principal plus any accumulated interest, resulting in faster growth over time.

How does compounding frequency affect my returns?

More frequent compounding means slightly higher returns. Daily compounding yields more than monthly, which yields more than annual compounding.

What is the Rule of 72?

The Rule of 72 estimates how long it takes to double your money. Divide 72 by the interest rate. At 8% interest, your money doubles in about 9 years (72/8 = 9).

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