Calculate compound interest growth on an investment, including regular monthly contributions, with a full breakdown of principal vs. interest earned.
Compound interest is interest calculated on both the initial principal and accumulated interest from previous periods, causing growth to accelerate over time versus simple interest.
More frequent compounding (daily or monthly vs. annually) produces slightly higher returns, since interest is calculated and added more often.
Yes, this calculator adds your regular monthly contribution on top of compound growth from your initial principal.
It's similar in concept — regular contributions compounding over time — though a dedicated SIP calculator may use fund-specific assumptions. This tool uses a standard fixed-rate compound growth model.
Compound interest is often called one of the most powerful forces in personal finance, because it causes money to grow at an accelerating rate over time — interest earns interest, which earns more interest, compounding on itself. This calculator computes exactly how a lump-sum investment (with optional ongoing monthly contributions) grows over time at a given interest rate and compounding frequency.
The basic compound interest formula for a lump sum is A = P(1 + r/n)^(nt), where P is the principal, r is the annual interest rate, n is the number of times interest compounds per year, and t is the number of years. When regular contributions are added, this calculator also computes the future value of that contribution stream using the standard future-value-of-annuity formula, then adds both together for the total future value.
The same annual interest rate produces slightly different results depending on how often it compounds. Daily compounding produces marginally higher returns than monthly, which in turn produces higher returns than annual compounding, because interest gets added to the principal more frequently, giving it more opportunities to itself earn interest within the same year. The difference is usually small for typical rates and timeframes, but it grows more noticeable over longer periods or at higher interest rates.
Adding a modest recurring contribution to an initial lump sum can dramatically change the final outcome over a long time horizon. This is because each new contribution starts compounding from the moment it's added, so contributions made early in the investment period have much longer to grow than contributions made near the end. This calculator's breakdown separates how much of your final total came from your original principal plus contributions, versus how much came purely from interest earned — a useful way to see compounding's effect concretely.
All calculations run directly in your browser — your financial details are never sent to a server or stored anywhere.
This calculator treats your initial principal and your recurring monthly contributions as two separate growth streams that are then added together. The principal grows using the standard compound interest formula on its own. The contribution stream is evaluated using the future-value-of-an-annuity formula, which accounts for the fact that each contribution is added at a different point in time and therefore compounds for a different length of time — the first contribution compounds for almost the entire period, while the final contribution barely compounds at all. Summing both streams gives the combined total future value shown in the results.
The progress bar beneath your results shows what portion of your final total came from money you actually put in (principal plus all contributions) versus money that was generated purely by compounding. Over short periods or at low interest rates, this bar leans heavily toward contributions. Over long periods — 15, 20, or 30 years — at a reasonable rate, the bar can shift to show that more than half the final value came from interest alone, which is a concrete illustration of why starting early matters more than the exact amount you start with.
A frequent error is assuming a stock market return (often quoted as an average like 10-12%) will apply smoothly and consistently every single year, when real returns vary significantly year to year even if they average out over a long enough horizon — this calculator shows the smooth, idealized version, not the bumpy real path. Another common mistake is forgetting to account for inflation, which erodes the real purchasing power of a future value even as the nominal number grows; a ₹50 lakh figure 25 years from now won't buy what ₹50 lakh buys today.
Simple interest is calculated only on the original principal for every period, so it grows at a constant, linear rate — ₹1,00,000 at 10% simple interest earns exactly ₹10,000 every single year. Compound interest instead recalculates the interest base each period to include previously earned interest, so the growth curve bends upward over time instead of staying flat. Over a short period the difference is small, but over 15-20+ years compound growth can produce a meaningfully larger total than simple interest at the same nominal rate, which is why almost all serious long-term investment products use compounding rather than simple interest.
This calculator is built to answer searches like "compound interest calculator with monthly deposit," "how much will my investment grow," "SIP vs lump sum compound growth," and "compound interest formula calculator." Because it supports both a one-time principal and ongoing monthly contributions together, it covers lump-sum investing, pure SIP-style investing, and the common hybrid case of starting with savings and then adding to it regularly.