Compound Interest Calculator
See how your money grows over time.
The Compound Interest Calculator shows how a lump sum grows over time as interest is repeatedly added to the balance and then earns interest of its own. You enter a starting amount, an annual interest rate, a number of years, and how often interest compounds, and the tool projects your future balance along with the total interest you earn.
It helps whenever you want a realistic picture of long-term growth, whether you are planning retirement savings, comparing bank accounts, or setting a goal for an investment. You can also add an optional monthly contribution to model regular deposits, and export the year-by-year schedule as a CSV file for your own records or spreadsheet.
Future balance
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Formula
A = P(1 + r/n)^(nt)How to use the compound interest calculator
- Enter your initial amount, the money you are starting with today.
- Type the annual interest rate as a percent, such as 5 for five percent per year.
- Set the number of years you plan to leave the money invested.
- Choose how often interest compounds: annually, monthly, or daily.
- Optionally add a monthly contribution to reflect regular deposits you will make.
- Read your future balance, total contributions, and total interest, then export the yearly schedule as CSV if you need it.
Worked example
Suppose you start with 10,000 dollars at a 5 percent annual rate, compounded monthly, for 10 years, with no extra contributions. Using A = P(1 + r/n)^(nt), the balance grows to about 16,470 dollars. Your total contribution stays at the original 10,000 dollars, so the total interest earned is roughly 6,470 dollars. Adding a 200 dollar monthly contribution would push the ending balance well above 47,000 dollars.
Common mistakes to avoid
- Entering the interest rate as a decimal like 0.05 instead of the percent value 5, which drastically understates growth.
- Confusing the annual rate with the compounding frequency and assuming monthly compounding means dividing the years instead of the rate.
- Forgetting that a monthly contribution adds to your total deposits, so not all of the final balance is interest.
- Ignoring taxes and inflation, which both reduce the real spending power of the projected balance.
- Assuming the interest rate is guaranteed when most real investments have returns that vary from year to year.
Frequently asked questions
What is compound interest?
Interest calculated on both your original principal and the interest already added, so growth accelerates over time.
How often should interest compound?
More frequent compounding (daily vs. yearly) yields slightly more, but the difference shrinks as rates get lower.
Does this calculator account for monthly deposits?
Yes. The optional monthly contribution field lets you model regular deposits. Those deposits are tracked separately as total contributions, so you can clearly see how much of the final balance came from your own money versus earned interest.
What is the difference between total contributions and total interest?
Total contributions is the sum of your initial amount plus every monthly deposit you make. Total interest is everything the account earns on top of that. Added together they equal your future balance.
How is this different from a loan calculator?
This tool projects how savings grow when interest works in your favor. A <a href="/tools/loan-calculator/">loan calculator</a> does the reverse, showing what you owe when interest accrues on a debt. For quick rate math, the <a href="/tools/percentage-calculator/">percentage calculator</a> can also help.