Compound Interest Calculator
Estimate future portfolio value with compound interest. Enter initial amount, monthly contribution, return rate, and years to see growth and interest earned.
Final value
$106,639.02
Total contributed
$70,000.00
Interest earned
$36,639.02
Yearly growth snapshot
| Year | Portfolio value |
|---|---|
| 1 | $16,919.19 |
| 2 | $24,338.58 |
| 3 | $32,294.31 |
| 4 | $40,825.16 |
| 5 | $49,972.70 |
| 6 | $59,781.53 |
| 7 | $70,299.43 |
| 8 | $81,577.68 |
| 9 | $93,671.22 |
| 10 | $106,639.02 |
What compound interest means
Compound interest means returns are earned on both your original principal and the gains already accumulated over time. In practice, this creates a snowball effect: the longer money stays invested, the larger the growth impact of each additional year. This is why consistent investing over many years can outperform irregular large deposits made late.
In this calculator, annual return is converted into a monthly growth rate and applied period by period. Monthly contributions are added continuously, making it useful for retirement planning, index fund investing, education savings, and long-term wealth targets.
Related terms: principal (starting capital), contribution (new cash added each month), return rate (expected annual growth), and future value (estimated ending balance).
How to interpret the results
Final value represents your projected portfolio at the chosen horizon. Total contributed is the sum of principal plus all contributions. The difference between those two values is interest earned, which helps you see how much growth came from compounding rather than deposits.
A useful visual check: if interest earned is small compared with total contributed, your time horizon may be too short or your contribution level may be too low for your target. If interest earned becomes larger than your contributions, compounding is doing the heavy lifting.
For planning quality, test multiple scenarios (conservative, base, optimistic). For example, compare 4%, 7%, and 9% annual returns with the same monthly contribution. This stress-testing approach gives a range instead of one fragile single-point estimate.
Important assumptions and limitations
This model assumes a constant return rate and steady monthly contributions. Real markets are volatile: returns vary year to year, and negative periods can happen. Fees, taxes, inflation, and contribution timing can materially change outcomes.
Use this page as a decision aid, not a guarantee. For higher-fidelity planning, pair these estimates with inflation-adjusted scenarios and net-return assumptions after fees and taxes. If you need formal advice, consult a licensed financial professional.