Compound Interest Calculator

Calculate how your savings or investments grow over time with compound interest. Supports monthly contributions and different compounding frequencies to help you plan for retirement, education, or any financial goal.

Examples

Retirement Savings — 30 Years

$10,000 initial investment with $500/month contributions at 7% for 30 years.

Initial Investment: $10,000
Annual Interest Rate: 7 %
Time Period: 30 years
Compounding Frequency: Monthly
Monthly Contribution: $500

Future Value

$691,150.47

Total Contributions

$190,000.00

Total Interest Earned

$501,150.47

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How It Works

Formula

A = P \left(1 + \frac{r}{n}\right)^{nt} + \text{PMT} \times \frac{\left(1 + \frac{r}{n}\right)^{nt} - 1}{r / n}

Variables, symbols and units

$A$: Future value at the end of the period
$P$: Initial investment (principal)
$\text{PMT}$: Monthly contribution (converted to per-period inside the formula)
$r$: Annual interest rate (decimal)
$n$: Compounding periods per year (12 monthly, 4 quarterly, 1 yearly)
$t$: Time period in years

Calculation method explained

Enter your initial investment, expected annual return, time period, and compounding frequency. Optionally add a monthly contribution. The calculator applies the compound interest formula to your principal and adds the future value of your regular contributions to show the total growth.

References and source material

Examples

Retirement Savings — 30 Years$10,000 · 7 % → $691,150.47

$10,000 initial investment with $500/month contributions at 7% for 30 years.

Initial Investment: $10,000
Annual Interest Rate: 7 %
Time Period: 30 years
Compounding Frequency: Monthly
Monthly Contribution: $500

Future Value: $691,150.47

Education Fund — 18 Years$5,000 · 6 % → $92,154.47

$5,000 lump sum with $200/month at 6% compounded monthly for 18 years.

Initial Investment: $5,000
Annual Interest Rate: 6 %
Time Period: 18 years
Compounding Frequency: Monthly
Monthly Contribution: $200

Future Value: $92,154.47

Lump Sum — No Contributions$50,000 · 8 % → $110,401.98

$50,000 invested at 8% compounded quarterly for 10 years.

Initial Investment: $50,000
Annual Interest Rate: 8 %
Time Period: 10 years
Compounding Frequency: Quarterly
Monthly Contribution: $0

Future Value: $110,401.98

Frequently Asked Questions

What is compound interest?

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 original amount, compound interest causes your money to grow exponentially over time — often called "interest on interest."

How does compounding frequency affect my returns?

More frequent compounding (e.g., monthly vs. yearly) means interest is calculated and added to your balance more often, so each subsequent calculation uses a slightly higher base. The difference is modest for typical rates but becomes more noticeable with higher rates or longer timeframes.

Why does this use a constant rate?

A constant rate keeps the compound-interest projection transparent: every period applies the same annual rate and compounding frequency. Real savings rates and investment returns can change over time, so treat the result as a scenario rather than a forecast.

Does this calculator account for taxes?

No — this shows gross growth before taxes. In practice, interest or investment gains may be taxable depending on account type and jurisdiction. The math here is the same compound-interest formula in every locale; it does not model local tax rules.

Is this accurate for stock market investments?

This calculator assumes a constant annual return, which is useful for simple scenarios but does not model real-world market volatility. Actual returns fluctuate year to year. Use the result as a hypothetical projection, not a guarantee.

Compound Interest Calculator

Retirement Savings — 30 Years

How It Works

Examples

Frequently Asked Questions

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