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Compound Interest Calculator with Monthly Deposits

This free compound interest calculator shows how your money grows when interest is added to the balance over and over. Choose the compounding frequency, add regular monthly deposits and see the result year by year.

By Debmedia Technologies LLP · Kolkata, India · Updated

What Is It and When Do You Need It?

Compound interest means you earn interest on your interest. It is why starting early matters so much for savings, pensions and investments, and also why debts can grow quickly.

Enter a starting amount, rate and time, plus optional monthly deposits. The tool shows the final balance and how much came from interest.

How to Use This Tool

  1. Enter the starting amount.
  2. Enter the yearly rate and the number of years.
  3. Choose how often interest is compounded and add a monthly deposit if you have one.
  4. Press Calculate.

How the Calculation Works

Without deposits the balance is A = P × (1 + r ÷ n)^(n t). With monthly deposits, the tool steps month by month: it adds the interest for the month on the whole balance, then adds the deposit. When the compounding is not monthly, it uses the equivalent monthly rate (1 + r ÷ n)^(n ÷ 12) − 1 so that the yearly effect is the same.

Worked Example

10,000 at 7% compounded monthly for 10 years grows to about 20,096. With a 200 monthly deposit added, it grows to about 54,714, of which 34,000 is your own money and about 20,714 is interest.

Common Uses

  • Planning savings and pensions.
  • Comparing deposit accounts.
  • Seeing the cost of debt over time.
  • Teaching how compounding works.

Tips and Common Mistakes

  • Time matters more than the rate: double the time and the effect is much more than double.
  • More frequent compounding helps a little.
  • Inflation and taxes reduce the real return.

Next, you may need the simple interest calculator, SIP calculator, fixed deposit calculator, CAGR calculator.

Everything runs in your browser. Nothing you type is uploaded, stored or sent to any outside service.

Frequently Asked Questions

Interest earned on both the original amount and the interest already added. Over long periods this makes money grow much faster than simple interest.
A = P × (1 + r ÷ n)^(n × t), where P is the starting amount, r is the annual rate, n is the number of compounding periods a year and t is the number of years.
Each deposit is added at the end of the month and then earns interest from the next month. For monthly deposits, the tool compounds monthly.
No. It assumes a constant rate. Real returns vary, and taxes and fees are not included.

Disclaimer: results are calculated in your browser from the numbers you enter. Check important results before you rely on them for money, health, safety or legal decisions.