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DayUtils

Compound Interest Calculator with Monthly Contributions

See how a starting amount and regular monthly deposits grow when interest earns interest. Choose yearly, quarterly, monthly, daily or continuous compounding and get the final balance, the interest earned and a year-by-year growth table.

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How to use the compound interest calculator

  1. Enter your starting amount.
  2. Enter a monthly contribution — or 0 if you are investing a single sum.
  3. Enter the yearly interest rate or expected return.
  4. Choose how many years to grow it.
  5. Pick how often interest compounds and whether you deposit at the start or end of each month.

The result shows your final balance, how much of it is your own money, and how much is interest. The table shows the balance at the end of every year.

The compound interest formula

A = P × (1 + r ÷ n)^(n × t)
  • A = final amount
  • P = starting amount
  • r = yearly rate as a decimal (7% = 0.07)
  • n = times interest compounds per year (12 for monthly)
  • t = years

With continuous compounding the formula becomes A = P × e^(r × t). Monthly contributions are added each month, and each one grows for the months that remain.

Worked example

Invest $10,000 at 7% for 10 years:

CompoundingFinal balance
Yearly$19,671.51
Monthly$20,096.61
Daily$20,136.18

Add $200 every month (monthly compounding) and the balance reaches about $54,714 — you put in $34,000 and interest adds about $20,700.

Getting the most from compound interest

  • Start early. Time is the biggest driver: money invested ten years sooner can end up worth roughly twice as much.
  • Contribute regularly. Small, steady deposits add up because every one starts compounding.
  • Reinvest earnings instead of taking them out.
  • Watch fees and taxes. A 1% yearly fee reduces your return just as much as a 1% lower rate.
  • Remember inflation. Use the inflation calculator to see what a future balance is worth in today’s money.

Savings accounts vs investments

Savings accounts and certificates of deposit pay a known rate. Stock and bond funds have no fixed rate — their long-run average returns go up and down year to year, so treat any rate you enter for them as an assumption, not a promise.

To plan a target, try the savings goal calculator. For retirement, see the retirement calculator. Indian investors can use the SIP calculator. Results are estimates — see our disclaimer.

Frequently asked questions

What is the compound interest formula?

For a single deposit: A = P × (1 + r ÷ n)^(n × t), where P is the starting amount, r the yearly rate as a decimal, n the number of times interest compounds per year and t the number of years. Regular deposits are added on top, each growing for the time it is invested.

How much will $10,000 grow in 10 years at 7%?

Compounded yearly it becomes $19,671.51; compounded monthly about $20,096.61; and daily about $20,136.18. Adding $200 a month as well (end of each month, monthly compounding) grows it to about $54,714, of which $34,000 is your own money.

Does compounding frequency matter much?

It matters a little. Going from yearly to monthly compounding adds about 2% to the final balance in the example above; going from monthly to daily adds only about 0.2%. The rate and the time invested matter far more.

What is the difference between simple and compound interest?

Simple interest is paid only on the original amount. Compound interest is also paid on interest already earned, so growth speeds up over time. Over long periods the difference becomes very large.

What does contribution timing change?

Deposits at the start of each month earn one extra month of interest compared with deposits at the end. Over many years this adds a little to the total.

What is the rule of 72?

A quick estimate: divide 72 by the yearly interest rate to get roughly how many years it takes money to double. At 7%, money doubles in about 72 ÷ 7 ≈ 10.3 years.

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