Compound Interest Calculator

How to use the compound interest calculator

1. Enter your starting amount, rate, and number of years.
2. Choose how often interest compounds.
3. Add a monthly contribution if you make regular deposits.
4. Read the future value and the year-by-year growth.

What compound interest is

Compound interest is interest earned on both your original money and the interest already added. Because each period's interest joins the balance and then earns interest itself, the growth speeds up over time. That is the "interest on interest" effect, and it is why compound interest matters so much for long-term saving and investing. This compound interest calculator shows the future value and traces the balance year by year.

The compound interest formula

The core formula is A = P(1 + r/n)^(nt): the amount A equals the principal P times one plus the rate r divided by the number of compounds per year n, all raised to n times the number of years t. More frequent compounding grows a little faster than annual compounding at the same rate, so daily compound interest edges ahead of monthly, which edges ahead of yearly. When you add a regular contribution, each deposit also compounds from the month it goes in.

Why the year-by-year table matters

The growth table shows how the balance builds each year, splitting what you put in from the interest earned. Early on, most of the balance is your own money. Later, the interest column grows and can overtake contributions, which is compounding at work. Watching the table makes the long-term payoff of starting early clear.

An estimate, not financial advice

This assumes a single, steady rate for the whole period. Real savings and investment rates change, and investments can fall as well as rise. Treat the result as a projection to compare scenarios, not a guarantee, and not financial advice.

FAQ

How does compound interest work?

Interest is added to your balance each period, and then future interest is charged on that larger balance. So you earn interest on your interest, which makes the balance grow faster over time.

What is the compound interest formula?

A = P(1 + r/n)^(nt), where P is the principal, r the annual rate, n the times it compounds per year, and t the years. The tool applies it and adds any monthly contributions.

Does compounding frequency change the result?

Yes, a little. Compounding monthly or daily grows slightly faster than annually at the same stated rate, because interest is added and starts earning sooner.

What is future value?

The future value is what your money grows to by the end: the starting amount plus all contributions plus all the interest earned. The headline figure is the future value.

Is my information private?

Yes. Everything is calculated in your browser and nothing you enter is uploaded or saved.