Compound Interest Calculator
Calculate compound interest and see the power of compounding on your investments.
with annually compounding
| Year | Compound | Simple | Extra Gain |
|---|---|---|---|
| Year 1 | ₹1.08 L | ₹1.08 L | +₹0 |
| Year 2 | ₹1.17 L | ₹1.16 L | +₹640 |
| Year 3 | ₹1.26 L | ₹1.24 L | +₹1,971 |
| Year 4 | ₹1.36 L | ₹1.32 L | +₹4,049 |
| Year 5 | ₹1.47 L | ₹1.40 L | +₹6,933 |
What is a Compound Interest Calculator?
A compound interest calculator is a free online tool that shows how your money grows when interest is reinvested year after year. Enter your principal, annual interest rate, tenure, and compounding frequency — the calculator instantly shows your final amount, total interest earned, and the breakdown over time.
Compound interest is famously called "the eighth wonder of the world" — interest that earns interest, building exponentially over time. Understanding it is the single most important step in personal finance: it's how every long-term investment (FD, PPF, mutual funds, real estate) actually grows.
Compound Interest Formula
The standard compound interest formula is:
- A = final amount (principal + interest)
- P = principal (initial investment)
- r = annual interest rate (as decimal, 0.08 for 8%)
- n = compounding frequency per year (1 = yearly, 4 = quarterly, 12 = monthly, 365 = daily)
- t = tenure in years
Total interest earned: I = A − P. The frequency of compounding makes a real difference — daily compounding earns roughly 0.5-1% more over the long term than yearly compounding at the same headline rate.
Simple vs Compound Interest
Simple interest pays only on the original principal. Compound interest pays on principal + accumulated interest. Over long horizons the difference is dramatic:
| Tenure (₹1L at 8%) | Simple Interest | Compound Interest (Yearly) | Difference |
|---|---|---|---|
| 5 years | ₹1,40,000 | ₹1,46,933 | +₹6,933 |
| 10 years | ₹1,80,000 | ₹2,15,892 | +₹35,892 |
| 15 years | ₹2,20,000 | ₹3,17,217 | +₹97,217 |
| 20 years | ₹2,60,000 | ₹4,66,096 | +₹2,06,096 |
| 30 years | ₹3,40,000 | ₹10,06,266 | +₹6,66,266 |
At 30 years, compound interest earns ~3x what simple interest earns. This gap widens with time and rate.
Compounding Frequency Comparison
Same 8% rate, same 10-year tenure, same ₹1 lakh principal — different compounding frequencies give different results:
| Compounding Frequency | Final Amount | Effective Annual Rate |
|---|---|---|
| Yearly (n=1) | ₹2,15,892 | 8.00% |
| Half-yearly (n=2) | ₹2,19,112 | 8.16% |
| Quarterly (n=4) | ₹2,20,804 | 8.24% |
| Monthly (n=12) | ₹2,21,964 | 8.30% |
| Daily (n=365) | ₹2,22,535 | 8.33% |
Over 10 years, daily compounding earns ₹6,643 more than yearly compounding on the same ₹1 lakh — for free, just by switching frequency. Most Indian bank FDs use quarterly compounding; PPF uses yearly.
The Rule of 72: How Fast Money Doubles
The Rule of 72 is a mental shortcut: divide 72 by your interest rate to estimate how many years it takes for money to double.
| Interest Rate | Years to Double (Rule of 72) | Real-world Example |
|---|---|---|
| 3% | 24 years | Savings account |
| 6% | 12 years | Bond fund |
| 7.1% | 10.1 years | PPF |
| 8% | 9 years | Hybrid mutual funds |
| 12% | 6 years | Equity mutual funds (avg) |
| 15% | 4.8 years | Top-tier stocks |
This is why returning 12% vs 8% changes outcomes so dramatically over a working life — your money doubles 5 times in 30 years at 12% vs 3.3 times at 8%.
Where to Apply Compound Interest in Real Life
- Equity mutual funds: SIPs and lumpsums grow via compounding of market returns. Use our SIP Calculator and Lumpsum Calculator.
- Fixed deposits: Quarterly compounding standard. See our FD Calculator.
- Recurring deposits: Quarterly compounding. RD Calculator.
- PPF: Yearly compounding at 7.1%. Use our PPF Calculator.
- NPS: Daily NAV-based compounding. NPS Calculator.
- Stock dividends: Reinvested dividends compound faster than withdrawn dividends.
- Real estate rentals: Reinvested rental income builds wealth via compounding.
The Cost of Waiting: Start Early Math
Two friends, A and B, both invest ₹10,000/month at 12% return. A starts at age 25 and stops at 35 (10 years). B starts at age 35 and continues till 60 (25 years). Who has more at 60?
| Investor | Total Invested | Corpus at Age 60 |
|---|---|---|
| A (started early, stopped early) | ₹12 lakh | ₹4.4 crore |
| B (started late, kept going) | ₹30 lakh | ₹1.9 crore |
A invested 2.5x less but ends up with 2.3x more. That's compounding rewarding the early start. The most important variable in long-term wealth is time, not the rate of return.
Frequently Asked Questions
What is the difference between simple and compound interest?
Simple interest is calculated only on the original principal. Compound interest is calculated on the principal plus accumulated interest. Over long horizons, compound interest grows much faster — at 8% over 30 years, compound interest earns roughly 3x what simple interest earns.
Which compounding frequency gives the highest returns?
Daily compounding gives the highest returns (effectively continuous compounding is the maximum). However, the difference between daily and monthly compounding is tiny (0.03-0.05% annually). For practical purposes, monthly or quarterly compounding captures most of the benefit. Yearly compounding is the worst.
What is the Rule of 72?
The Rule of 72 is a mental shortcut to estimate how long it takes money to double at a given interest rate: divide 72 by the rate. At 8%, money doubles in 9 years. At 12%, in 6 years. The rule is a close approximation of the actual logarithmic doubling time.
How does compound interest work in mutual funds?
Mutual funds compound through NAV growth. As the underlying assets earn returns (dividends, interest, capital gains), the NAV rises. Holding the fund means your existing units grow in value — that's compounding. Reinvesting dividends accelerates compounding further.
Can compound interest work against me?
Yes — credit card debt, personal loans, and BNPL schemes use compound interest against you. Credit card unpaid balances compound at 36-42% annually — turning a ₹50,000 balance into ₹1 lakh+ in 2 years if unpaid. Always pay credit card bills in full to avoid this.
What are some real Indian examples of compounding?
PPF: ₹1.5L/year for 15 years at 7.1% = ₹40.68 lakh maturity. Equity SIP: ₹10K/month for 30 years at 12% = ₹3.5 crore. NPS: ₹5K/month for 30 years at 10% = ₹1.13 crore. These all happen automatically; you just need to start and stay invested.
How do I calculate compound interest manually?
Use the formula A = P × (1 + r/n)^(n×t). Example: ₹1 lakh at 8% compounded quarterly for 5 years = 100,000 × (1 + 0.08/4)^(4×5) = 100,000 × (1.02)^20 = 100,000 × 1.486 ≈ ₹1,48,600. The calculator above does this automatically.
Is compound interest the same as CAGR?
CAGR (Compound Annual Growth Rate) is the annualized rate of return assuming compound growth. It's the "reverse" — given a starting and ending amount, what compound rate produced that growth? Useful for comparing investments of different durations.
Do compound interest calculations change with tax?
Pre-tax compound interest is what calculators show. Post-tax compounding depends on the instrument: PPF/SGB compound tax-free; FDs are taxed at slab rate annually (TDS); equity mutual funds are taxed only at redemption (LTCG over ₹1.25L/year at 12.5%). Tax-efficient instruments compound much faster.
What return rate should I use in compound interest calculator?
For Indian context: 7-8% for safe instruments (FD, PPF, NPS Tier 1 conservative), 10-13% for equity mutual funds (long-term average), 6-8% for debt funds, 8-10% for SGB. Never assume 15%+ for long horizons — Indian equity markets have averaged 11-13% over 20+ year periods.
Pro Tip: The more frequently interest compounds, the more you earn. Monthly compounding beats yearly compounding, and daily compounding beats monthly!