Calculate compound interest, investment growth, total interest and final balance with our free calculator. Compare daily, monthly and yearly compounding.
Your starting balance or principal
Decimals are fine, e.g. 7.5 years
Optional recurring deposit — leave at 0 to skip
Contributions are assumed to be made at the end of each period; results are estimates based on these assumptions
Enter values above to see results
A = P × (1 + r/n)^(n×t)AFinal amountPPrincipal (initial amount)rAnnual interest rate (decimal)nCompounding frequency per yeartTime in yearsCompound interest is interest calculated on both the initial principal and the accumulated interest from previous periods. Unlike simple interest (which only earns on the principal), compound interest grows exponentially over time. When you add recurring contributions, each deposit compounds for whatever time remains until the end of the investment period, so the calculator values contributions individually rather than simply adding them to the final total.
Compound interest is interest calculated on both your original principal and the interest that balance has already earned. Each time interest is added — daily, monthly, or yearly, depending on the compounding frequency — it becomes part of the balance that earns interest going forward. Over long periods this compounding effect can meaningfully outpace simple interest, which is why compound interest is central to how savings accounts, investments, and loans grow.
Enter your starting investment, annual interest rate, investment period, and compounding frequency, then add a recurring contribution if you plan to keep depositing money. The calculator applies the compound interest formula automatically and updates in real time, showing your final balance, total contributions, total interest earned, effective annual rate, and estimated doubling time. Recurring contributions are valued individually based on how long each one has left to grow, not simply added to the total.
| Compounding Frequency | Effect at the Same Nominal Rate |
|---|---|
| Daily (365×/year) | Interest is added every day, so the effective annual rate is the closest to the theoretical maximum for a given nominal rate. |
| Weekly (52×/year) | Very close to daily compounding — the effective rate is only marginally lower. |
| Monthly (12×/year) | The most common frequency for savings accounts and loans; noticeably higher effective rate than annual compounding. |
| Quarterly (4×/year) | Common for some bonds and certificates of deposit; a modest step up from semi-annual. |
| Semi-annually (2×/year) | Interest is added twice a year; used by some bonds and government securities. |
| Annually (1×/year) | Interest is added once a year, so the effective annual rate equals the nominal rate. |
| Feature | Compound Interest vs Simple Interest |
|---|---|
| How interest is calculated | Compound: on the principal plus all previously earned interest. Simple: on the original principal only. |
| Previous interest included? | Compound: yes, interest earns interest. Simple: no, each period's interest is based on the same original amount. |
| Growth over time | Compound: grows exponentially, with the gap widening the longer money is invested. Simple: grows linearly at a constant amount per period. |
| Common uses | Compound: savings accounts, most investments, and many loans. Simple: some short-term loans and basic interest calculations. |
A lump sum left to grow with no further contributions.
Ends at about $22,196.40 — $12,196.40 of that is interest, more than the original deposit.
At 8%, the Rule of 72 says money doubles in about 9 years — this example more than doubles in 10.
The same $10,000 at 8% for 10 years, compounded at different intervals.
Moving from annual to daily compounding adds about $664 over 10 years.
Frequency helps, but the rate and the time horizon matter far more.
$10,000 initial investment, 8% annual rate, $500 added every month, over 20 years, compounded monthly.
The account reaches about $343,778.24 — $120,000 of that was contributed and roughly $213,778.24 is interest.
Regular contributions can add far more to the final balance than the initial lump sum, especially over longer periods.
This calculator lets you compare compounding frequencies, test how a recurring contribution changes your outcome, and see a year-by-year growth chart so the effect of compounding is easy to follow rather than abstract. That makes it useful for comparing savings accounts and investment options, estimating how a monthly contribution habit adds up, and understanding roughly how the true cost of compounding works on the lending side too.
A few mistakes come up often. Some people confuse the nominal annual rate with the effective annual rate, which is always slightly higher once compounding is applied more than once a year. Others forget to set a contribution frequency after entering a contribution amount, so no recurring deposits are included. It's also easy to underestimate how much investment duration matters compared to compounding frequency, or to compare two rates without checking whether they compound the same way. Finally, remember that calculator output is an estimate based on the assumptions you enter — it is not a guaranteed investment return.
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