Compound Interest Calculator
Year-by-year growth
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What Is Compound Interest?
Compound interest is interest calculated not only on your original investment but also on the interest it has already earned. Each compounding period, your balance grows a little — and the next period's interest is charged on that larger balance. Over time, this snowball effect means your money grows faster and faster, which is why Albert Einstein is often (perhaps apocryphally) credited with calling compound interest the most powerful force in finance.
This free compound interest calculator shows you exactly how that snowball builds. It is ideal for anyone planning long-term savings: retirement funds, a child's education pot, a house deposit, or simply comparing what different banks and savings schemes will pay you over the years. Enter your starting amount, the annual rate, the time horizon and how often interest compounds, and you will see the final balance, the total interest earned, and a year-by-year growth table. The maths is universal, so it works with any currency.
How to Use This Compound Interest Calculator
- Enter your initial investment. The lump sum you are starting with today.
- Enter the annual interest rate. Use the nominal yearly rate quoted by the bank or scheme (for example 12 for 12% per year).
- Enter the time period in years. Compounding rewards patience — even a couple of extra years makes a visible difference.
- Choose the compounding frequency. Yearly, quarterly, monthly or daily — the more frequent the compounding, the slightly higher the return.
- Click "Calculate Growth". You will see the final balance, how much of it is your own money, how much is interest, and the full year-by-year breakdown.
Worked Example: Rs 500,000 at 12% for 10 Years, Compounded Monthly
The compound interest formula is:
where P is the principal, r is the annual rate as a decimal, n is the number of compounding periods per year, and t is the number of years. Working through our example step by step:
- Monthly rate: r/n = 0.12 ÷ 12 = 0.01
- Total periods: n × t = 12 × 10 = 120
- Growth factor: (1.01)120 = 3.300387
- Final balance: 500,000 × 3.300387 = Rs 1,650,193.45
- Interest earned: 1,650,193.45 − 500,000 = Rs 1,150,193.45
Notice that the interest (Rs 1,150,193.45) is more than double the original investment — your money more than tripled. For comparison, the same deposit compounded only once a year would grow to Rs 1,552,924.10. Monthly compounding earns you roughly Rs 97,269 extra over the decade, purely from the frequency effect. Try switching the frequency selector in the tool to see the gap for yourself.
Tips to Make Compounding Work Harder for You
- Start as early as you can. Time is the biggest lever in compounding — money invested at 25 has decades longer to snowball than money invested at 35.
- Prefer more frequent compounding. When two products quote the same annual rate, the one compounding monthly or daily wins.
- Reinvest, don't withdraw. Every rupee of interest you take out stops earning its own interest. Leave gains in to keep the snowball rolling.
- Add regular contributions. A monthly top-up on top of your lump sum accelerates growth dramatically — even small, steady deposits compound.
- Watch out for fees and taxes. Account charges and tax on interest income quietly eat into the effective rate; compare products on what you actually keep.
- Be realistic about rates. A calculator assumes the rate never changes. Stress-test your plan with a lower rate too, so a rate cut doesn't wreck your goal.
Frequently Asked Questions
What is the difference between simple and compound interest?
Simple interest is calculated only on the original principal every period, so it grows in a straight line. Compound interest is calculated on the principal plus all previously earned interest, so growth accelerates over time. On a Rs 500,000 deposit at 12% for 10 years, simple interest would pay Rs 600,000 — but compounding monthly pays Rs 1,150,193.45, nearly double.
Which compounding frequency gives the highest return?
For the same nominal annual rate, more frequent compounding always gives a slightly higher return: daily beats monthly, monthly beats quarterly, and quarterly beats yearly. The differences are modest over short periods but become meaningful over decades, so when comparing two savings products at the same rate, pick the one that compounds more often.
Does compounding frequency really make a big difference?
It makes a real but secondary difference — the rate and the time horizon matter far more. In our worked example, moving from yearly to monthly compounding added about Rs 97,269 over ten years on Rs 500,000. Worth having, but an extra 1% on the interest rate or five more years of saving would dwarf that gain. Use the tool's frequency selector to quantify it for your own numbers.
What if I add money every month instead of investing a lump sum?
This calculator models a single lump-sum deposit. Regular monthly contributions actually grow even faster in practice, because each new deposit starts compounding from the day it lands. If your plan is to save monthly, the figure here is a conservative baseline — your real result with top-ups would be higher. Many banks offer recurring-deposit products designed exactly for that pattern.
Is the growth shown by this calculator guaranteed?
No — it is a mathematical projection, not a promise. It assumes the interest rate stays constant and no money is withdrawn. Real products can change rates, charge fees, or (for market-linked investments) go up and down. Use the result for planning and comparison, and re-run it with a lower rate to see how your goal holds up under less generous conditions.