Investment Growth Calculator
See how compound interest and regular contributions grow your money over time. Enter your starting balance, expected rate of return, and how much you plan to add — this free tool projects your future balance instantly, with no signup required.
Investment details
The S&P 500's long-run historical average is roughly 7–10% annually.
Future balance
$0
after 10 years
Where it came from
- Initial deposit $0
- Total contributions $0
- Interest earned $0
Want to actually track this?
BudgetWise's Investments feature tracks real contributions and growth automatically — no spreadsheet, no re-running a calculator every month.
Start freeHow compound interest works
Compound interest is interest earned on interest. When your investment grows, that growth becomes part of your balance — and next period, you earn a return on the original amount and the gains it already produced. Over short periods the effect is small, but over years and decades it's the difference between money that grows in a straight line and money that grows on a curve.
The core formula is A = P × (1 + r/n)^(n × t), where P is your principal, r is the annual rate as a decimal, n is how many times per year interest compounds, and t is the number of years. Add regular contributions on top, and each one starts compounding from the moment it lands — which is why this calculator simulates your balance period by period instead of relying on a single formula.
Two levers matter more than people expect: time and consistency. A smaller amount invested for twice as long often outgrows a larger amount invested for half the time, and steady monthly contributions — even modest ones — tend to compound into a meaningfully larger balance than sporadic lump sums of the same total size, simply because the money has more time in the market.
Frequently asked questions
What is compound interest?
Compound interest is interest calculated on both your original investment and on the interest it has already earned. Instead of earning a flat amount each period, your balance grows faster over time because past gains keep earning their own returns.
How is compound interest calculated?
Future value equals your principal multiplied by (1 + rate/n) raised to the power of (n × years), where n is how many times per year interest compounds. If you add regular contributions, each one starts compounding from the moment it's deposited, which is what this calculator simulates period by period.
How does compounding frequency affect growth?
More frequent compounding (daily or monthly vs. annually) grows your balance slightly faster at the same stated annual rate, because interest starts earning its own interest sooner. The effect is real but usually modest — a few tenths of a percent difference in total growth over long periods.
What's a realistic rate of return to use?
The S&P 500's long-run historical average return is roughly 7–10% annually before inflation. High-yield savings accounts and CDs typically return far less (4–5% or lower), while a diversified stock portfolio has historically landed in that 7–10% range over long holding periods. Using an unrealistically high rate (15%+) will overstate your projection.
Does this calculator account for taxes or inflation?
No — this is a gross growth projection based on the rate of return you enter. It doesn't subtract taxes on gains or adjust for inflation, so treat the result as a nominal (not real, after-tax) estimate.
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