Compound Interest Calculator
Enter a starting amount, monthly deposits and a rate to see how your savings grow over time.
Final balance
17,175.24
Total contributed
13,000.00
Interest earned
4,175.24
Year-by-year breakdown
| Year | Contributed | Interest | Balance |
|---|---|---|---|
| 1 | 2,200.00 | 79.05 | 2,279.05 |
| 2 | 3,400.00 | 223.53 | 3,623.53 |
| 3 | 4,600.00 | 436.81 | 5,036.81 |
| 4 | 5,800.00 | 722.38 | 6,522.38 |
| 5 | 7,000.00 | 1,083.97 | 8,083.97 |
| 6 | 8,200.00 | 1,525.44 | 9,725.44 |
| 7 | 9,400.00 | 2,050.90 | 11,450.90 |
| 8 | 10,600.00 | 2,664.64 | 13,264.64 |
| 9 | 11,800.00 | 3,371.17 | 15,171.17 |
| 10 | 13,000.00 | 4,175.24 | 17,175.24 |
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How it works
- Enter your initial amount and how much you plan to add every month.
- Set the annual interest rate, the number of years and how often interest compounds.
- Read the final balance, total contributed and interest earned, and open Options for the year-by-year table.
Frequently asked questions
- How is compound interest calculated here?
- The balance is advanced one compounding period at a time: each period the current balance earns interest at the annual rate divided by the number of periods per year, and your deposits for that period are added on top. This means interest is also earned on previously earned interest, which is what makes long-term growth accelerate.
- What is the difference between simple and compound interest?
- Simple interest is paid only on the original amount, so growth is a straight line. Compound interest is paid on the whole balance including previously earned interest, so growth curves upward over time. Over one year the difference is small, but over decades compounding can multiply the outcome several times over.
- What is the Rule of 72?
- It is a mental shortcut for doubling time: divide 72 by the annual return to estimate how many years it takes for money to double. At 6 percent that is roughly 12 years; at 9 percent, roughly 8. The rule stays remarkably accurate for rates between about 4 and 12 percent — use the calculator to check the exact figure.
- Does the compounding frequency make a big difference?
- Less than most people expect. Moving from yearly to monthly compounding at the same nominal rate adds a fraction of a percent to the effective annual yield. The rate itself, the time horizon and how much you contribute matter far more than the frequency.
- Are taxes and inflation included?
- No. The result is the nominal balance before any taxes on interest or investment gains, and it is not adjusted for inflation. To estimate real purchasing power, a common shortcut is to subtract the expected inflation rate from your annual return before running the numbers.
About this tool
This compound interest calculator shows how a starting amount plus regular monthly deposits grows over time. Enter an initial balance, a monthly contribution, an annual interest rate, a time horizon in years and a compounding frequency, and it immediately reports the final balance, the total you contributed and how much of the result is interest. A year-by-year table under Options shows the same figures at every step, which makes it easy to see when growth starts to accelerate.
The math runs entirely in your browser: the balance is advanced one compounding period at a time, earning the periodic rate and collecting your deposits along the way. Nothing you enter is sent to a server, so you can experiment with real figures from your own accounts without any of it leaving your device.
People use it to answer concrete questions: what a retirement account might hold in thirty years, what a monthly savings habit is really worth, whether an extra hundred per month matters over a long horizon (it usually does, dramatically), or how a lump sum compares against steady contributions. It also works in reverse as a sanity check on advertised investment projections — if a product’s claimed outcome needs a 15 percent annual return to be true, you will see that here in seconds.
Two habits make the results more meaningful. Use a realistic long-term rate rather than one recent good year — broad stock index funds have historically returned roughly 7 to 10 percent per year before inflation, while savings accounts earn far less. And if you want the answer in today’s purchasing power, subtract expected inflation from the rate before calculating; the nominal figure otherwise flatters the outcome.