Compound Interest Calculator
Calculate how your investment grows over time with compound interest and regular contributions.
Enter investment details and click Calculate
Compound Interest Calculator — Grow Your Wealth Exponentially
Compound interest is often called the eighth wonder of the world — and for good reason. It is interest calculated not just on your initial investment (principal) but also on all the interest you've previously earned. This "interest on interest" effect creates exponential growth that dramatically accelerates wealth building over time.
The difference between compound interest and simple interest becomes staggering over long periods. ₹1,00,000 invested at 12% simple interest grows to ₹3,40,000 in 20 years. The same amount at 12% compound interest (annually) grows to ₹9,64,629 — nearly 3x more! This is the power of compounding at work.
The key insight: time is the most important variable in compounding. Starting just 5 years earlier can mean lakhs more in your final corpus. If you start investing ₹5,000/month at age 25, you'll have far more by age 60 than someone who starts at 30 investing the same amount — because those extra 5 years of compounding make an enormous difference.
What is Compound Interest?
Compound interest is interest calculated not just on the original principal but also on all previously accumulated interest — creating an 'interest on interest' effect that generates exponential growth over time. Often called the eighth wonder of the world, compounding is the core mechanism behind long-term wealth creation.
- Unlike simple interest (calculated only on principal), compound interest accelerates growth exponentially — ₹1,00,000 at 12% grows to ₹3,40,000 with simple interest in 20 years but ₹9,64,629 with compound interest.
- Compounding frequency matters: the more often interest is compounded (daily > monthly > quarterly > annually), the higher the effective annual return on the same nominal rate.
- The Rule of 72 is a quick mental shortcut: divide 72 by the annual interest rate to find approximately how many years it takes to double your money (e.g., at 12%, money doubles in 6 years).
- Time is the most powerful variable in compounding — starting a ₹5,000/month SIP at age 25 instead of 35 at 12% p.a. results in a corpus more than 1.8 times larger by age 60.
How to Use This Calculator
- Enter your initial investment amount (principal)
- Enter the expected annual interest/return rate
- Select compounding frequency (monthly for SIP/mutual funds, annual for FDs)
- Enter the investment period in years
- Optionally, enter a monthly contribution amount (for SIP-style investing)
- Click Calculate to see your final corpus, total invested, and total interest earned
Compound Interest Formula
- A = Final amount (maturity value)
- P = Principal (initial investment)
- r = Annual interest rate (as decimal, e.g. 0.12 for 12%)
- n = Compounding periods per year (12 for monthly, 4 for quarterly)
- t = Time in years
- PMT = Monthly contribution amount
- Example = ₹1,00,000 at 12% compounded monthly for 10 years
- A = 1,00,000 × (1 + 0.12/12)^(12×10)
- A = 1,00,000 × (1.01)^120 = ₹3,30,039
Rule of 72 — Quick Doubling Time Calculator
The Rule of 72 is a mental shortcut to find how many years it takes to double your money at a given interest rate:
- At 6%: 72 ÷ 6 = 12 years to double
- At 9%: 72 ÷ 9 = 8 years to double
- At 12%: 72 ÷ 12 = 6 years to double
- At 18%: 72 ÷ 18 = 4 years to double
Practical Example — Starting Early vs Starting Late
Investor A starts at age 25, invests ₹5,000/month for 35 years at 12% p.a.
Investor B starts at age 35, invests ₹5,000/month for 25 years at 12% p.a.
- Investor A total invested: ₹21,00,000 | Final corpus: ₹1,76,49,569
- Investor B total invested: ₹15,00,000 | Final corpus: ₹94,88,090
- Difference: ₹81,61,479 — just by starting 10 years earlier!
Key Terms
- Principal
- The initial amount you invest or deposit.
- Compounding Frequency
- How often interest is calculated and added to the principal (daily, monthly, quarterly, annually).
- CAGR (Compound Annual Growth Rate)
- The annualized rate of return for an investment over a specific period.
- SIP (Systematic Investment Plan)
- Regular monthly investments in mutual funds — the best way to harness compounding.
- Effective Annual Rate (EAR)
- The actual annual rate accounting for compounding — always higher than the nominal rate.
Tips to Maximize Compound Interest
- Start investing as early as possible — even ₹1,000/month at age 20 beats ₹10,000/month at age 40
- Never withdraw early — reinvesting all returns is what creates exponential growth
- Increase your SIP amount by 10-15% every year (step-up SIP)
- Index funds and diversified equity mutual funds have historically given 12-15% CAGR in India
- Choose monthly compounding over annual when available — it earns slightly more
- Account for inflation — a 12% return with 6% inflation gives only 6% real return
Frequently Asked Questions
Simple interest is calculated only on the original principal. Compound interest is calculated on the principal plus all previously earned interest. For example, ₹1,00,000 at 10% for 3 years: Simple Interest = ₹30,000 total. Compound Interest = ₹33,100 total — 10% more! The gap grows dramatically over longer periods.
The Rule of 72 is a quick mental math trick: divide 72 by the annual interest rate to find how many years it takes to double your money. At 12%, money doubles in 6 years (72÷12=6). At 9%, it takes 8 years. At 6%, it takes 12 years. Very useful for quick investment comparisons.
More frequent compounding gives slightly higher returns. Daily > Monthly > Quarterly > Annual compounding. For ₹1 lakh at 12% for 10 years: Annual compounding = ₹3,10,585; Monthly compounding = ₹3,30,039; Daily compounding = ₹3,32,000. The difference is modest unless the investment is very large.
SIP (Systematic Investment Plan) in mutual funds leverages compound interest by regularly investing a fixed amount. Each month, your investment buys mutual fund units. As the NAV grows (ideally at 12-15% CAGR historically), and as dividends are reinvested, compounding works on your growing corpus. Starting a ₹5,000/month SIP at 12% for 20 years creates a corpus of ₹49,95,745 from just ₹12 lakh invested!
For long-term compounding (10+ years), equity mutual funds (especially index funds) have historically given 12-15% CAGR in India — the best real returns after inflation. For medium-term (3-5 years), PPF gives ~7.1% tax-free. For short-term (1-3 years), bank FDs give 6.5-7.5%. ELSS mutual funds give equity returns plus Section 80C tax benefits — an excellent option for salaried investors.
At 12% compounded annually: ₹1,00,000 × (1.12)^10 = ₹3,10,585. At 12% compounded monthly: ₹3,30,039. If you also add ₹5,000/month SIP during these 10 years (at 12% monthly compounding): final corpus ≈ ₹11,61,695. The additional monthly contributions dramatically accelerate growth.
Every year you delay costs you exponentially more than the year itself. ₹1 lakh invested at 25 becomes ₹93 lakh by 65 at 12%. The same ₹1 lakh invested at 35 becomes only ₹30 lakh — 3x less! The 10-year delay cost ₹63 lakh from a single ₹1 lakh investment. Time is the most powerful factor in compounding — start today, even with small amounts.