Compound Interest Calculator With Monthly Contributions

Your estimate

—

estimated future value

Total contributions—
Interest earned—
Effective annual yield—

Your contributions
Interest earned

Year-by-year growth
Year	Contributions	Interest	Balance

Estimates only. Figures are rounded and assume the inputs stay the same for the whole period.

Estimates only: Results are based on the numbers you enter and simplified assumptions. They are not a loan offer, rate quote or financial advice. Actual terms depend on the lender and your situation.

How compound interest works

Compound interest is interest earned on both your original deposit and the interest that has already been added to it. Each period, the balance grows a little, and the next period’s interest is calculated on that larger balance. Over short periods the effect is small; over decades it becomes the largest part of your balance.

This calculator adds your monthly contributions at the end of each month and compounds interest at the frequency you choose. The year-by-year table shows how the interest share of your balance accelerates over time.

The compound interest formula

For a single deposit: A = P × (1 + r/n)^n×t

A — ending balance
P — starting principal
r — annual interest rate (decimal)
n — compounding periods per year
t — years

Example: $5,000 at 4% compounded monthly for 15 years grows to about $9,100 with no additional deposits. Add $300 a month and the balance reaches roughly $83,000, of which about $24,000 is interest.

Three ways to make compounding work harder

Start early. Time is the most powerful input; the last years of growth are the largest.
Contribute automatically. A recurring transfer on payday removes the temptation to skip a month.
Earn a competitive rate. Moving idle cash to a high-yield savings account or a CD can multiply what it earns compared with a traditional savings account.

Read our full guide on how compound interest works, or use the investment growth calculator to model long-term investing with inflation.

Frequently asked questions

What is the compound interest formula?

For a single deposit, A = P × (1 + r/n)^(n×t), where P is the principal, r the annual rate as a decimal, n the number of compounding periods per year and t the number of years. Regular contributions add a second term for the future value of a series of deposits.

How often is interest compounded on a savings account?

Many banks compound interest daily and credit it monthly. Because the advertised APY already reflects compounding, you can enter the APY here and choose annual compounding for a close estimate.

What rate should I use?

For a savings account or CD, use its current APY. For long-term investing, use a conservative assumption and remember that investment returns are not guaranteed and vary from year to year.

What is the Rule of 72?

Divide 72 by the annual interest rate to estimate how many years it takes money to double. At 6%, money doubles in about 12 years; at 4%, about 18 years.

Learn more

Checking vs. Savings Account: Differences and How to Use Both — Checking vs. savings accounts compared: how each works, interest, fees, access and insurance, plus a simple system for using both to manage money.
How Much Emergency Savings Should You Have? A Complete Emergency Fund Guide — How much emergency savings you need, how to calculate your target, where to keep it and a step-by-step plan to build an emergency fund — even on a tight budget.
Financial Planning for Beginners: How to Make a Financial Plan — Financial planning for beginners: set goals, track net worth, budget, build an emergency fund, pay off debt, save for retirement and get insured.
How Does a CD Work? Certificates of Deposit Explained — How certificates of deposit work: fixed rates and terms, early withdrawal penalties, maturity, CD ladders and how CDs compare with high-yield savings.

Compound Interest Calculator