Compound Interest Calculator
See how your money grows with the power of compounding — free, no account required, and your numbers never leave your device. Enter your initial investment, annual interest rate, time period, and optional monthly contributions to get your future value and a year-by-year growth schedule.
Added at the start of each month
Future Value
$37,506.06
Total Invested
$22,000
Interest Earned
$15,506
Return
+70.5%
Growth Breakdown
This calculator provides estimates for illustrative purposes only and does not constitute financial advice. Results assume a constant interest rate, no taxes, and no fees. Actual investment returns will vary.
How It Works
Enter your starting amount
Type in any lump sum you already have, or leave it at zero if you're starting from scratch with regular contributions.
Set your rate and time
Enter the annual interest rate you expect and how many years you plan to invest. Choose how often interest compounds.
Add monthly contributions
Optionally enter how much you'll add each month. This models a regular savings plan on top of your initial deposit.
See your future value instantly
Results update in real time as you type — including interest earned, total return, and a year-by-year schedule. Nothing leaves your browser.
How to Use the Compound Interest Calculator
- Enter your initial investment — the amount you're starting with today.
- Set the annual interest rate — your expected yearly return or savings rate.
- Choose the time period in years — how long you plan to leave the money invested.
- Select a compound frequency — how often interest is added (monthly is most common for savings accounts).
- Optionally enter a monthly contribution to model regular deposits.
- See your future value and interest breakdown update immediately.
- Click Show year-by-year growth schedule to see how your balance builds each year.
Understanding the Results
| Result | What it means |
|---|---|
| Future Value | The total amount you'll have at the end of the period, including all contributions and interest earned. |
| Total Invested | Your initial deposit plus all monthly contributions — the money you actually put in. |
| Interest Earned | Future value minus total invested — the growth generated purely by compounding. |
| Return | Interest earned as a percentage of total invested — your overall gain. |
What Is Compound Interest?
Compound interest means you earn interest not only on your original deposit but also on the interest you've already earned. Over time this creates a snowball effect — each year's growth is slightly larger than the last, which is why Albert Einstein (apocryphally) called it "the eighth wonder of the world."
The standard formula is: A = P(1 + r/n)nt, where:
- A — the future value of the investment
- P — the initial principal
- r — annual interest rate (as a decimal)
- n — number of times interest compounds per year
- t — time in years
This calculator extends the basic formula to support regular monthly contributions, giving you a realistic picture of a consistent savings or investment plan.
Compounding Frequency Explained
The more frequently interest compounds, the more you earn — though the difference narrows at higher frequencies. Here's a quick comparison for a $10,000 principal at 7% for 10 years (no contributions):
| Frequency | Future Value |
|---|---|
| Annually | $19,672 |
| Quarterly | $20,016 |
| Monthly | $20,097 |
| Daily | $20,136 |
Features
- Your data stays private: All calculations run entirely in your browser — nothing is uploaded or stored on any server.
- No account required: Open the page and start calculating straight away.
- Real-time results: Future value and breakdown update instantly as you type — no button to press.
- Five compound frequencies: Daily, monthly, quarterly, semi-annually, and annually.
- Monthly contributions: Model a regular savings plan alongside your initial deposit.
- Year-by-year schedule: See exactly how your balance, contributions, and interest grow each year.
- Visual breakdown: A bar chart shows the proportion of contributions versus interest at a glance.
Frequently Asked Questions
Is my financial data stored or shared?
No. All calculations run locally in your browser using JavaScript. The values you enter are never sent to or stored on any server.
What is compound interest?
Compound interest means you earn interest on both your original deposit and on the interest already credited to your account. Over time this creates exponential growth — often called "interest on interest."
What does compound frequency mean?
Compounding frequency is how many times per year interest is calculated and added to your balance. More frequent compounding (e.g. daily vs. annually) earns slightly more because each period's interest is calculated on a slightly larger balance.
How accurate is this calculator?
The calculator applies the standard compound interest formula and accurately models monthly contributions added at the start of each month. Results are estimates — they assume a constant rate, no taxes, and no fees. Actual returns will vary.
What is the Rule of 72?
The Rule of 72 is a quick estimate: divide 72 by the annual interest rate to find how many years your money takes to double. At 7%, it doubles in roughly 10.3 years (72 ÷ 7). The calculator's year-by-year schedule shows you the exact doubling point.
What's the difference between compound and simple interest?
Simple interest is calculated only on the original principal, so growth is linear. Compound interest is calculated on the growing balance, so growth is exponential. Over long periods the difference is enormous — compound interest is what drives long-term wealth building.