Compound Interest Calculator

A Compound Interest Calculator is a financial tool that computes the future value of an investment or loan based on the principle of compounding — where interest is calculated on both the initial principal and the accumulated interest from previous periods. It uses the standard compound interest formula A = P(1 + r/n)^(nt), where A is the final amount, P is the principal, r is the annual interest rate, n is the compounding frequency per year, and t is the time in years. This calculator helps investors, savers, and borrowers instantly determine how their money grows or what they owe over time.

The compound interest formula A = P(1 + r/n)^(nt) calculates the total amount after compounding. Here, A represents the final amount (principal + interest), P is the initial principal or investment amount, r is the annual interest rate (in decimal, e.g., 8% = 0.08), n is the number of times interest is compounded per year (1 for annual, 4 for quarterly, 12 for monthly, 365 for daily), and t is the number of years. The compound interest earned is then CI = A - P. For example, ₹1,00,000 invested at 8% compounded monthly for 5 years yields A = 1,00,000 × (1 + 0.08/12)^(12×5) = ₹1,48,985.

The compounding frequency significantly impacts your returns — the more frequently interest is compounded, the higher the final amount. For example, on ₹1,00,000 at 10% for 10 years: annual compounding yields ₹2,59,374; semi-annual yields ₹2,65,330; quarterly yields ₹2,68,506; monthly yields ₹2,70,704; and daily compounding yields ₹2,71,740. While the difference may seem small in the short term, it becomes substantial over longer periods and larger amounts. This calculator lets you compare different compounding frequencies side by side.

The Rule of 72 is a quick mental math shortcut to estimate how long it takes for an investment to double at a given compound interest rate. Simply divide 72 by the annual interest rate to get the approximate doubling time in years. For example, at 8% interest, your money doubles in approximately 72 ÷ 8 = 9 years. At 12%, it doubles in about 6 years. Conversely, you can divide 72 by the number of years to find the required interest rate: to double money in 6 years, you need approximately 12% annual return. This rule works best for interest rates between 6% and 10%.

Simple interest is calculated only on the original principal amount throughout the investment period, using the formula SI = P × R × T / 100. Compound interest, on the other hand, is calculated on the principal plus accumulated interest, resulting in exponentially higher returns over time. For example, ₹1,00,000 at 10% for 10 years: simple interest gives ₹2,00,000 (interest of ₹1,00,000), while annual compound interest gives ₹2,59,374 (interest of ₹1,59,374). The difference of ₹59,374 demonstrates the power of compounding, which becomes even more dramatic over longer periods — making compound interest the preferred basis for long-term investment planning.

In India, banks calculate compound interest on fixed deposits (FDs) using quarterly compounding for most tenures, as mandated by RBI guidelines. The formula applied is A = P(1 + r/4)^(4t). Savings accounts typically use daily compounding on the end-of-day balance, credited quarterly. For recurring deposits (RDs), interest is compounded quarterly as well. This means the effective annual yield on an FD advertised at 7% per annum is actually higher — approximately 7.19% when compounded quarterly. Use this calculator to determine the exact maturity value of your FD, RD, or savings account deposits.

This Compound Interest Calculator can be used for investment planning by entering your lump sum investment as the principal, expected annual return rate, and investment duration. For SIP (Systematic Investment Plan) planning, you can calculate the compounded returns on each monthly installment separately or use the future value of annuity formula. For example, a monthly SIP of ₹10,000 at 12% expected return for 15 years grows to approximately ₹50.46 lakh, with total investment of only ₹18 lakh — the remaining ₹32.46 lakh is pure compounding effect. This tool helps you set realistic financial goals and compare different investment options.