What is compound interest?

It is interest calculated on both your original amount and the interest already added. Over time the balance grows faster than with simple interest.

How does compounding frequency change the result?

More frequent compounding adds interest sooner, so it earns interest a little earlier. Daily compounding gives a slightly higher balance than yearly at the same rate.

How are contributions handled?

Each contribution is added at the end of a compounding period and then earns interest for the rest of the term.

Does this include tax or inflation?

No. The result is before tax and fees and is not adjusted for inflation, so the real spending power may be lower.

What rate should I use?

That is your choice. Use a rate you think is realistic for your savings or investment, and remember real returns vary year to year.

Can I save or share my result?

Yes. You can copy, share a link that reopens the same scenario, download a text summary, or print the page.

Compound interest calculator

Compound interest is interest on your interest. Enter a starting amount, a rate, and how long you save — then watch the balance build.

Enter a starting amount, an annual rate, a term, how often interest compounds, and an optional regular contribution. You get the final balance split into deposits and interest, plus a growth chart.

Final balance

$31,998.32

Deposits Interest

Total deposited: $22,000.00
Total contributions: $12,000.00
Total interest: $9,998.32

The bars show each year's balance: deposits at the bottom, interest stacked on top. Interest grows faster over time because it builds on earlier interest.

How does it work?

Contributions are added at the end of each compounding period. With a 0% rate the balance is simply principal plus contributions.

Compound interest formula

FV = P\left(1+\tfrac{r}{n}\right)^{nt} + PMT\cdot\frac{\left(1+\tfrac{r}{n}\right)^{nt}-1}{\tfrac{r}{n}}

FV: Future value (final balance).
P: Starting principal.
r: Annual interest rate as a decimal.
n: Compounding periods per year.
t: Number of years.
PMT: Contribution added each period.

10,000 at 5% compounded monthly for 10 years grows to about 16,470 with no extra deposits.

Method & sources

The interest rate stays the same for the whole term. Contributions are added at the end of each compounding period. Taxes, fees, and inflation are not included.

Sources

Where this method comes from — use these references to understand the formula, assumptions, and limits.

Compound interest — investor bulletin — U.S. Securities and Exchange Commission (Investor.gov), verified 2026-06-10

How we calculate

The interest rate stays the same for the whole term.
Contributions are added at the end of each compounding period.
Taxes, fees, and inflation are not included.
Results are estimates for planning, not a forecast or financial advice.

Rounding

Balances are rounded to two decimals for display. The calculation uses full precision.

What this calculator does

It projects how a balance grows when interest is added back and then earns interest itself. You can include regular contributions, which is how most people actually save.

How to use it

Enter your starting amount.
Enter the annual interest rate you expect.
Choose the term in years and how often interest compounds.
Add a regular contribution if you plan to keep saving.

A worked example

Start with 10,000 at 5% compounded monthly for 10 years. With no extra deposits it grows to about 16,470. Add 100 each month and the balance reaches roughly 32,000 — and most of the gap above your deposits is interest.

What the result means

The final balance is your deposits plus the interest earned. The longer the term and the more often interest compounds, the larger the interest share becomes.

Common mistakes

Entering a monthly rate in the annual rate field. Use the yearly rate.
Expecting a fixed rate to match real-world investments, which vary.
Forgetting that inflation reduces what the final balance can buy.

When it's useful

Planning long-term savings, comparing how compounding frequency affects growth, or seeing the effect of adding a small monthly amount over many years.

FAQ

What is compound interest?: It is interest calculated on both your original amount and the interest already added. Over time the balance grows faster than with simple interest.
How does compounding frequency change the result?: More frequent compounding adds interest sooner, so it earns interest a little earlier. Daily compounding gives a slightly higher balance than yearly at the same rate.
How are contributions handled?: Each contribution is added at the end of a compounding period and then earns interest for the rest of the term.
Does this include tax or inflation?: No. The result is before tax and fees and is not adjusted for inflation, so the real spending power may be lower.
What rate should I use?: That is your choice. Use a rate you think is realistic for your savings or investment, and remember real returns vary year to year.
Can I save or share my result?: Yes. You can copy, share a link that reopens the same scenario, download a text summary, or print the page.

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