Compound Interest Calculator

Finance Guide

Power of Compounding

The Formula

A = P(1 + r/n)^(nt) where P = principal, r = annual rate, n = compounding frequency per year, t = time in years.

Rule of 72

Divide 72 by the annual rate to find doubling time. At 12%: 72÷12 = 6 years. More compounding periods = slightly faster doubling.

Time Is Everything

₹1L at 12% for 10 years = ₹3.1L. For 20 years = ₹9.6L. For 30 years = ₹29.6L. Compounding rewards patience, not size.

Frequency Matters

Monthly compounding beats annual by 0.6–1% effective yield at typical rates. Daily vs monthly is negligible - pick high rate over high frequency.

Compound interest is the process of earning interest on both the principal amount and the previously accumulated interest. Unlike simple interest, which is calculated only on the original sum, compound interest grows exponentially over time. The formula A = P(1 + r/n)^nt was formalized in Europe during the 17th century, though ancient Indian mathematicians - including those who authored texts like the Arthashastra around 300 BCE - understood the concept of interest on interest in lending practices.

Why Compounding Frequency Matters

The frequency of compounding - daily, monthly, quarterly, or annually - significantly affects the final corpus. A principal of Rs. 1,00,000 invested at 8% annual interest compounded monthly for 10 years yields approximately Rs. 2,21,964, compared to Rs. 2,15,892 with annual compounding. Indian investors using PPF, EPF, FDs, and mutual fund SIPs experience compounding in action. SEBI-regulated mutual funds report CAGR figures that reflect compounding, making this calculator essential for financial planning.

Applications in Indian Financial Planning

Understanding compound interest is critical for aspirants preparing for UPSC, SSC, and bank exams such as IBPS and SBI PO, where CI problems appear regularly in quantitative aptitude sections. RBI mandates that banks display annualised interest rates incorporating compounding for consumer clarity. Whether you are planning an SIP, comparing FD offers, or estimating education fund growth, this calculator helps you make data-driven decisions quickly.

Compound Interest Questions

Compound interest is calculated on both the principal and accumulated interest - 'interest on interest'. Simple interest is calculated only on the original principal. Example: ₹1,00,000 at 10% for 5 years - Simple Interest = ₹50,000; Compound Interest (annually) = ₹61,051. The difference grows dramatically over longer periods - which is why compound interest is so powerful for long-term investing.

A = P × (1 + r/n)^(n×t), where A = maturity amount, P = principal, r = annual rate (decimal), n = compounding frequency per year (annual=1, quarterly=4, monthly=12, daily=365), t = time in years. CI = A – P. Example: ₹1,00,000 at 8% compounded quarterly for 3 years: A = ₹1,26,899.

More frequent compounding produces higher returns. Example: ₹1,00,000 at 10% for 1 year - Annual: ₹1,10,000; Quarterly: ₹1,10,381; Monthly: ₹1,10,471; Daily: ₹1,10,517. Most Indian bank FDs compound quarterly. Mutual funds compound daily through NAV-based pricing.

The Rule of 72 estimates how long it takes to double an investment: Years to double = 72 ÷ Interest Rate. At 6% → 12 years; at 8% → 9 years; at 12% → 6 years; at 18% → 4 years. Accurate for rates between 6–20%. Also works in reverse: to double money in 8 years you need approximately 9% return.

₹1,00,000 compounded annually over 10 years: at 6% → ₹1,79,085; at 8% → ₹2,15,892; at 10% → ₹2,59,374; at 12% → ₹3,10,585; at 15% → ₹4,04,556; at 18% → ₹5,23,384. Even a 2–3% difference in returns makes an enormous difference over long investment horizons.

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