Compound Interest Calculator
Use this free compound interest calculator to see how your savings can grow over time. Enter a starting amount, a monthly deposit, an interest rate and a time period to get your future balance in seconds.
Show year by year breakdown
| Year | Contributions | Interest | Balance |
|---|
Estimates only. Assumes a fixed rate, deposits at the end of each month and no taxes or fees.
Example: $10,000 plus $200 a month at 7% compounded monthly grows to about $325,159 after 30 years. You only put in $82,000. The other $243,159 is interest.
How to Use This Compound Interest Calculator
- Currency: pick the currency you save in. The math works the same for all of them.
- Initial deposit: the amount you start with today.
- Monthly contribution: how much you plan to add each month. Enter 0 if you will not add more.
- Annual interest rate: the yearly rate your account or investment pays.
- Years: how long you plan to let the money grow.
- Compounding: how often interest is added to your balance.
After that, the results show your future balance, how much you paid in and how much came from interest. Then open the year by year breakdown to see how growth speeds up over time.
Why Use a Compound Interest Calculator?
First of all, doing the math by hand gets complicated as soon as you add monthly deposits. A compound interest calculator does it instantly, so you can test different plans side by side. For example, you can see what happens if you save $50 more each month, choose a higher rate or wait five more years.
In addition, it is a great motivation tool. Seeing a real number for your future balance makes it much easier to stick with your savings habit today.
What Is Compound Interest?
Compound interest is interest earned on both your original money and on the interest you have already earned. In other words, your interest starts earning its own interest.
By contrast, with simple interest you only earn on the starting amount. With compound interest, however, the base keeps getting bigger, so the growth gets faster every year. This is why starting early matters so much, even with small amounts. You can learn more about saving and investing basics from Investor.gov, run by the U.S. Securities and Exchange Commission.
Compound Interest Formula
The standard formula for compound interest, without regular deposits, is:
A = P × (1 + r / n)n × t
- A is the final amount
- P is the starting amount (principal)
- r is the yearly interest rate as a decimal, so 5% is 0.05
- n is how many times interest compounds per year
- t is the number of years
Worked example: you invest $10,000 at 5% compounded monthly for 10 years. That gives A = 10,000 × (1 + 0.05 / 12)120, which equals about $16,470. You earned $6,470 in interest without adding another dollar.
Compound Interest Calculator Examples
These examples were worked out with this compound interest calculator, using monthly deposits, 7% a year and monthly compounding, with no starting balance.
| Monthly Savings | 10 Years | 20 Years | 30 Years | 40 Years |
|---|---|---|---|---|
| $100 | $17,308 | $52,093 | $121,997 | $262,481 |
| $250 | $43,271 | $130,232 | $304,993 | $656,203 |
| $500 | $86,542 | $260,463 | $609,985 | $1,312,407 |
Why starting early matters: someone who saves $300 a month from age 25 to 65 at 7% ends up with about $787,444. If they wait until 35 to start, they end up with about $365,991. In other words, that ten year delay cuts the final balance by more than half, even though they only put in $36,000 less.
Compound Interest vs Simple Interest
Here is how $10,000 grows at 5% a year with each method. As a result, the gap gets wider the longer you wait.
| Years | Simple Interest | Compound Interest (yearly) | Difference |
|---|---|---|---|
| 10 | $15,000 | $16,289 | $1,289 |
| 20 | $20,000 | $26,533 | $6,533 |
| 30 | $25,000 | $43,219 | $18,219 |
How Compounding Frequency Changes Your Results
Generally, the more often interest compounds, the more you earn, although the difference is small. This table shows $10,000 at 5% for 10 years.
| Compounding | Final Balance |
|---|---|
| Annually | $16,289 |
| Quarterly | $16,436 |
| Monthly | $16,470 |
| Daily | $16,487 |
As you can see, the interest rate and the number of years matter far more than how often interest compounds.
The Rule of 72
Want a quick estimate without a calculator? Divide 72 by your yearly interest rate. Then the answer is roughly how many years it takes for your money to double. For example, at 6% your money doubles in about 12 years, and at 9% it doubles in about 8 years.
Tips to Make Compound Interest Work for You
- Start early. Time is the most powerful part of the formula.
- Add a little every month. Regular deposits grow much faster than a one time amount.
- Build your safety net first. An emergency fund stops you from pulling money out early.
- Make saving automatic. The 20% savings bucket in the 50/30/20 budget rule is a simple way to do it.
- Reinvest your interest. Leave earnings in the account so they keep compounding.
- Watch out for debt. Compound interest works against you on credit cards. Our guide on how to get out of debt can help.
Frequently Asked Questions
How does compound interest work?
Compound interest pays you interest on your original money and on the interest you have already earned. Over time, this creates a snowball effect where your balance grows faster each year.
How often is interest compounded?
It depends on the account. Savings accounts often compound daily or monthly, while some bonds and CDs compound quarterly or yearly. More frequent compounding gives slightly higher returns.
Is compound interest good or bad?
It is good when you are saving or investing because your money grows faster. However, it works against you on debt, such as credit cards, because unpaid interest also starts to earn interest.
What is a realistic interest rate to use?
Use the rate your savings account actually pays, or a cautious long term estimate for investments. Rates change over time, so it helps to test a few different numbers.
Does this calculator include taxes or fees?
No. It shows growth before taxes, fees and inflation. Your real result may be lower, so use it as a planning guide rather than a promise.
Disclaimer: This compound interest calculator is for educational purposes only. Results are estimates and are not financial advice. Real returns depend on rates, fees, taxes and inflation. Please read our full disclaimer.