Compound Interest Calculator

What Does This Calculator Calculate?

• Principal Amount: the initial amount you invest or deposit, before any interest.
• Total Interest Earned: the interest accumulated over the chosen time period, based on the rate and compounding frequency selected.
• Future Value: the principal plus all accumulated interest — the estimated total value at the end of the period.

What Is Compound Interest?

Compound interest is interest calculated on a principal amount plus any interest that has already been added to it, so that later interest is earned on a progressively larger base. This differs from simple interest, which is always calculated on the original principal alone. The two factors that most influence how much a sum grows under compounding are how often interest is added to the balance (the compounding frequency) and how long the money stays invested (the time period).

How Compound Interest Works

At the end of each compounding period, interest for that period is calculated on the current balance and then added to it. In the next period, interest is calculated on this new, larger balance — meaning interest itself starts earning further interest. Over many periods, this produces a curve that rises faster than the straight-line growth you'd see with simple interest, because each period's starting balance is a little larger than the last.

Compound Interest Formula

This calculator estimates future value using the standard compound interest formula:

A = P × (1 + r/n)^(n×t)

• A = estimated future value
• P = principal amount
• r = annual interest rate, expressed as a decimal
• n = number of compounding periods per year (12 monthly, 4 quarterly, 2 half-yearly, 1 annually)
• t = time period in years

From this, Total Interest Earned = A − P. This calculator applies this formula year by year to build the annual breakdown table, which produces the same final result as applying the formula once over the full period.

How Interest Rate Affects Compound Growth

Holding principal, time and compounding frequency constant, a higher assumed annual rate produces a higher estimated future value — and the effect compounds over long periods rather than growing in a straight line. For ₹1,00,000 over 10 years with quarterly compounding:

• At an assumed 6%: Future Value ≈ ₹1,81,402
• At an assumed 8%: Future Value ≈ ₹2,20,804
• At an assumed 10%: Future Value ≈ ₹2,68,506

You can verify these by entering each rate into the calculator above with Principal ₹1,00,000, Time 10 years and Quarterly compounding. As always, these rates are assumptions for illustration, not promised returns from any specific product.

Compound Interest for Savings

This calculator can help illustrate long-term growth scenarios for goals such as building an emergency fund, saving toward a child's education, or planning for retirement. Because it uses an assumed fixed annual rate, it is best used as a way to compare different scenarios — for example, the effect of starting five years earlier, or saving a larger monthly amount — rather than as an exact prediction of what any single savings product will pay.

Compound Interest and Fixed Deposits

Some deposit products use periodic compounding similar in principle to the formula above, but the exact compounding convention, payout options and applicable rate depend entirely on the bank or institution and the specific product terms. This calculator does not claim to reproduce any particular bank's fixed deposit calculation exactly — for a dedicated FD estimate, see our FD Calculator.

Compound Interest and Investments

For market-linked investments such as mutual funds or equities, there is an important distinction to keep in mind: this calculator computes mathematical compounding using a rate you choose to assume, while actual investment returns are driven by market performance and are never a guaranteed fixed percentage. It can be useful for illustrating "what if my investment grew at X% a year," but the resulting figure is a mathematical projection, not investment advice or a promised outcome. To model a monthly recurring investment specifically, see our SIP Calculator; for a one-time lump-sum investment, see our Lumpsum Calculator.

This calculator is designed for the four inputs shown above — principal, rate, time and compounding frequency — and does not model recurring contributions such as monthly deposits. If you want to estimate the growth of regular monthly investments rather than a single lump sum, our SIP Calculator is built for that purpose.

Common Compound Interest Calculation Mistakes

• Entering a monthly rate as if it were annual, or vice versa — always check whether a quoted rate is per annum.
• Confusing a percentage with a decimal — 10% should be entered as 10, not 0.10, in this calculator's rate field.
• Selecting the wrong compounding frequency for the product you're trying to model.
• Confusing months with years in the time period field.
• Comparing a simple-interest quote with a compound-interest estimate as if they were the same thing.
• Assuming a fixed rate will continue indefinitely, especially for market-linked investments where rates and returns change.
• Ignoring taxes or fees, which this calculator does not include and which can meaningfully reduce actual take-home returns.
• Treating investment returns as guaranteed, when only some fixed-rate products offer a contractually fixed rate.
• Ignoring inflation when interpreting a large nominal future value.
• Comparing two products calculated with different conventions (for example, different compounding frequencies) as if the headline rates were directly comparable.