Compound interest is the mechanism by which your investment returns generate their own returns. Rather than earning a fixed amount on your original principal each year, your balance grows against an ever-expanding base — turning modest, consistent contributions into substantial long-term wealth.
This calculator projects the future value of an investment given an initial lump sum, ongoing monthly contributions, an expected annual rate of return, and a chosen compounding frequency — with an optional inflation adjustment to show real, purchasing-power-adjusted growth.
The Variables This Calculator Measures
- Initial Investment — the lump sum you start with (can be ₦0 if contributing monthly only).
- Monthly Contribution — the amount added each month; consistency drives long-term outcomes more than the amount itself.
- Annual Interest Rate — your assumed yearly return, which varies by asset class.
- Compounding Frequency — how often interest is calculated and added to your balance (annually, monthly, daily, etc.).
- Inflation Rate — an optional input that converts your nominal future value into today’s purchasing power.
Compound Interest Calculator
Project your portfolio growth with recurring deposits and optional inflation tracking
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Calculation Methodology
This tool computes a monthly-stepped compounding schedule, applying contributions and interest month by month rather than a single end-of-period formula, which correctly captures the effect of recurring contributions:
Each month: Balance = (Balance + Contribution) × (1 + Monthly Rate)
Total Interest = Final Balance − Total Contributions
Real Value = Final Balance ÷ (1 + Inflation Rate)^Years
For a lump sum with no contributions and no inflation adjustment, this reduces to the standard compound interest formula: A = P(1 + r/n)nt, where A is future value, P is principal, r is the annual rate, n is compounding frequency, and t is years.
The Rule of 72
A quick mental shortcut for estimating how long an investment takes to double: divide 72 by the annual interest rate. At a 10% annual return, an investment doubles in approximately 7.2 years; at 15%, roughly 4.8 years. This approximation holds reasonably well for rates between about 6% and 20% and is useful for sanity-checking the calculator’s output.
Worked Examples
Lump sum: ₦100,000 invested at 15% annually for 10 years, compounded monthly, with no further contributions, grows to approximately ₦444,067 — over ₦344,000 of that is compound growth alone.
Monthly contributions: ₦20,000 contributed every month for 20 years at 15% (monthly compounding) results in total contributions of ₦4,800,000 against a future value of approximately ₦13,322,000 — meaning ₦8,522,000, more than the total amount contributed, comes purely from growth.
Both examples assume a constant annual rate for illustration. Real markets fluctuate year to year; the underlying mechanic — time and reinvestment compounding growth — remains the same regardless of the specific rate achieved.
Disclaimer: This calculator is for educational and informational purposes only and does not constitute financial advice, an investment recommendation, or a guarantee of future returns. All figures are based on a fixed rate you supply and do not reflect real-world market volatility, fees, or taxes, which can materially affect actual outcomes. Investments carry risk, including possible loss of principal — past performance and projected returns never guarantee actual results. Consult a licensed financial advisor before making investment decisions.