Compound Interest Calculator
See how an initial principal grows with compound interest and regular contributions. Choose your compounding and contribution frequency, and review a year-by-year breakdown and growth chart.
Last reviewed: 2026-07-29
Results
Enter your figures above and select Calculate. Results appear here with clear labels — never colour alone.
What is compound interest?
Compound interest is the interest earned on both your initial principal and the interest that has already accumulated. Each compounding period, the interest is added to your balance, and the next period's interest is calculated on this larger amount. This creates exponential growth — the longer your money compounds, the faster it grows.
Albert Einstein is often quoted as calling compound interest "the eighth wonder of the world." Whether or not he said it, the principle is sound: time and consistency are the most powerful factors in long-term wealth accumulation.
Compound interest formula
- Periodic Rate = Annual Rate ÷ Periods per Year
- Balance = Principal × (1 + Periodic Rate) ^ Total Periods
- With contributions, each deposit compounds from its entry point
- Total Interest = Final Balance − Principal − Total Contributions
- Inflation-Adjusted = Balance ÷ (1 + Inflation Rate) ^ Years
This calculator uses an iterative period-by-period calculation so that different contribution and compounding schedules are handled accurately, rather than a single closed-form formula.
Worked example
$10,000 invested at 7% annual interest, compounded monthly, for 10 years, with $100 monthly contributions at the end of each month.
- Periodic Rate = 7% ÷ 12 = 0.583% per month
- Total Periods = 10 × 12 = 120 months
- Final Balance ≈ $29,600 (principal + contributions + interest)
- Total Contributions = $10,000 + ($100 × 120) = $22,000
- Total Interest ≈ $7,600
Compare with the ROI calculator for return-on-investment calculations.
How to use this calculator
Enter your initial principal, annual interest rate and investment period. Optionally add regular contributions and choose the contribution and compounding frequency. The calculator iterates period by period to produce an accurate result, then displays a year-by-year table and a growth chart.
If you enter an inflation rate, the inflation-adjusted future value shows what the final balance is worth in today's purchasing power.
Interpreting the results
The percentage from contributions shows how much of the final balance comes from money you put in versus how much comes from interest earned. Over short periods, contributions dominate; over long periods, interest can overtake contributions — this is the power of compounding.
These are mathematical estimates based on a fixed interest rate. Real investment returns vary, can be negative, and are not guaranteed. This calculator does not constitute investment advice.
Limitations and common mistakes
- Assuming fixed returns. Real investments do not grow at a constant rate. Volatility is normal.
- Ignoring fees and taxes. Investment fees and taxes reduce actual returns. Adjust your rate accordingly.
- Forgetting inflation. A 7% nominal return at 3% inflation is only a 4% real return. Use the inflation-adjusted figure.
- Overestimating contributions. Be realistic about what you can consistently contribute over the full period.
- Confounding with ROI. Compound interest projects growth; ROI measures past performance. See the ROI calculator.
Frequently asked questions
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Disclaimer
Results from this calculator are estimates for general information only and are not financial, accounting, tax, investment or legal advice. Verify important figures with a qualified professional. Read our full disclaimer.