Compound Interest Calculator
Calculate how your investments grow over time with the power of compound interest.
Enter values above to see results
How to use this calculator
Enter your assumptions above and review how projected outcomes change as you adjust contribution amount, rate of return, timeline, or withdrawal values. Testing conservative, moderate, and optimistic scenarios can help you understand a realistic range of possible results.
Start by using realistic estimates based on your personal situation. If unsure about expected returns, use historical average returns but recognize that past performance does not guarantee future results. You can experiment with different assumptions by changing one variable at a time and observing how each factor affects your outcome. This helps build intuition for how contributions, time horizon, and rate of return interact.
Assumptions and limitations
Calculator outputs are educational projections, not guarantees. Real outcomes can differ due to market volatility, inflation, taxes, fees, and personal circumstances. Use these estimates as planning support and combine them with broader research before making financial decisions.
This calculator assumes consistent investment behavior, reinvested returns, and doesn't account for withdrawals beyond those specified or emergency changes to your plan. For a personalized financial plan, consult with a qualified financial advisor who can review your complete situation. Our goal is educational—to help you understand the mechanics of compound growth and the impact of key variables on long-term wealth building.
How compound interest works
Compound interest means that a return can be earned on both the original balance and prior returns that remain invested. Time, contribution consistency, the assumed rate of return, and compounding frequency all influence the projection.
A calculator is useful because it makes the trade-offs visible. A modest contribution made consistently may have more effect over a long horizon than a short-term attempt to find a perfect entry point. Test conservative, moderate, and optimistic rates rather than relying on one number. Also compare the ending balance with total deposits so that an assumed rate does not hide the role of saving discipline, fees, inflation, or a change in the investment timeline.
Formula and inputs
For a starting balance with periodic contributions, the projection combines the future value of the initial amount with the future value of each contribution. With periodic compounding, the core relationship is A = P(1 + r/n)^(nt), then contributions are added using the same compounding assumption.
Enter the starting balance, recurring contribution, assumed annual rate, number of years, and compounding frequency. Keep the contribution timing consistent with the calculator setting because deposits made at the beginning or end of a period can produce different results.
Worked planning example
Suppose an investor starts with $10,000, contributes $200 each month, assumes a 7% annual return compounded monthly, and keeps the plan for ten years. The projection is an illustration of a consistent saving habit, not a forecast of market performance.
| Input or result | Example | What it means |
|---|---|---|
| Starting balance | $10,000 | Amount invested at the start |
| Monthly contribution | $200 | Additional amount invested each month |
| Assumed annual return | 7% | Illustrative annual rate before fees and taxes |
| Time horizon | 10 years | Period over which compounding is modelled |
| Total contributions | $34,000 | Starting balance plus scheduled deposits |
How to interpret the result
Compare the projected ending value with total contributions to see how much of the illustration comes from deposits and how much comes from the assumed growth rate. Re-run the calculation with a lower rate or a shorter horizon to understand the risk of relying on a single optimistic assumption.
Limitations to keep in mind
The calculation assumes a steady return and regular deposits. Actual markets do not deliver the same return each year, and the result does not automatically account for taxes, investment fees, withdrawal rules, missed contributions, or changes in risk tolerance.
Use this tool to test assumptions, not to predict a guaranteed outcome. Financial markets, inflation, taxes, fees, account rules, and personal circumstances can change a real-world result. For decisions that depend on your full financial situation, consider speaking with a qualified professional.
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What is Compound Interest?
Compound interest is the interest calculated on the initial principal and also on the accumulated interest from previous periods. It’s often called “interest on interest” and is one of the most powerful concepts in investing.
How to Use This Calculator
Enter your initial investment amount, monthly contribution, expected annual interest rate, and the number of years you plan to invest. The calculator will instantly show your projected total value, total contributions, and interest earned.
Sources and assumptions
The examples on this page are mathematical illustrations based on the inputs shown. Results are not forecasts or guarantees; fees, taxes, inflation, market changes, timing, and personal circumstances can materially change real outcomes.