Compound Interest Calculator

Choose a display currency, enter the amount invested initially, and add an optional recurring contribution. The contribution amount is deposited monthly, quarterly, or yearly according to the selected frequency.

Enter a nominal annual rate, choose how often interest compounds, and set a whole-number duration in years. The projection updates automatically.

The main result shows the ending balance. Supporting results separate the money contributed from growth produced by compounding and show the effective annual rate.

Open the projection breakdown to inspect the balance chart, contribution-versus-growth mix, yearly schedule, and CSV export.

Compound interest is growth calculated on the original principal and on growth already added to the balance.

After interest is credited, it becomes part of the balance used at the next compounding boundary. Repeating that process creates growth on earlier growth.

Investor.gov describes compound growth as earning a return on money invested and on the return that money has already earned.

The entered annual percentage is treated as a nominal rate. The calculator divides it by the number of compounding periods in one modeled year.

The effective annual rate measures the result of applying that periodic rate for a full year. It can be higher than the nominal rate when compounding occurs more than once per year.

FINRA notes that annual percentage yield includes the effect of compounding, while a basic or nominal rate does not. Check which type of rate a real account or product publishes before comparing it with this calculator.

With the same nominal annual rate, more frequent compounding credits growth sooner and slightly increases the effective annual rate.

The difference depends on the rate, duration, and balance. Compounding frequency does not turn an unrealistic return assumption into a reliable forecast.

The table uses a $1,000 initial balance, a 12% nominal annual rate, no contributions, and one modeled year.

A monthly contribution is added 12 times per year, a quarterly contribution four times, and a yearly contribution once.

Contributions are deposited at period end. When a contribution and interest credit share a boundary, the calculator credits interest first and then adds the contribution.

A beginning-of-period contribution would receive one additional period of growth and therefore produce a higher ending balance. This calculator deliberately uses end-of-period timing.

Contribution frequency and compounding frequency can differ. For example, you can contribute monthly while interest compounds quarterly.

The engine processes both event schedules in chronological order through a fixed 365-day modeled year. Daily compounding credits 365 times; monthly and quarterly events occur at their modeled period ends.

The fixed-year convention is used because the calculator accepts a duration rather than actual start and end dates.

Total contributions include the initial investment and every recurring deposit.

Growth from compounding equals the projected ending balance minus total contributions.

The yearly schedule reconciles each opening balance with contributions and growth to produce the ending balance, which becomes the following year's starting balance.

The effective annual rate describes the rate mechanics only. It does not include the effect of new contributions.

Simple interest is calculated only on the original principal. Compound interest also applies to growth previously credited to the balance.

The two methods can produce similar results over a short period or at a low rate, but the difference generally grows with time and repeated compounding.

This tool models compound growth and does not provide a separate simple-interest schedule.

The Rule of 72 estimates doubling time by dividing 72 by an annual percentage rate. At 9%, the estimate is about eight years.

It is a mental shortcut, not the calculation used by this tool. Exact doubling time depends on the rate convention and compounding frequency.

Recurring contributions also change the balance, so a contribution-based projection should be evaluated with the full schedule rather than the Rule of 72 alone.

A fixed-rate deposit product may apply a stated rate for a defined period, but market investments do not normally grow at one smooth percentage every year.

Actual returns can be positive or negative, and the order of returns affects the final balance. The calculator cannot reproduce market volatility from one constant rate.

Investor.gov warns that fees and expenses reduce the amount left earning a return. This model excludes those costs, along with taxes and inflation.

The calculation, chart data, yearly schedule, and CSV export are produced locally in the browser.

The projection is suitable for comparing mathematical scenarios, contribution plans, and compounding assumptions.

Do not treat the result as a guaranteed return, financial recommendation, account statement, or substitute for the terms and disclosures of a real product.