About the Compound Interest Calculator
Tezmy's Compound Interest Calculator shows how money grows when interest earns interest. Enter a starting amount, how much you'll add each month, the expected yearly return and how many years you'll save. You'll see the final balance, how much of it you put in and how much came from interest, plus a chart and a year-by-year table. Use it to plan savings, retirement, index fund investing or a child's education fund, and to see why starting early makes such a big difference.
Updated October 2026
How to use the Compound Interest Calculator
- 1Enter your starting amount and how much you'll add each month.
- 2Enter the yearly return or interest rate.
- 3Choose how many years and how often interest compounds.
- 4Read your final balance and see the growth year by year.
How compound interest works
With compound interest, the interest you earn is added to your balance, and next time you earn interest on that interest too. 1,000 at 8% a year becomes 1,080 after one year, 1,166 after two and about 2,159 after ten. The longer you leave it, the faster it grows.
Why starting early matters
Time is the most powerful part of compounding. Someone who saves 200 a month from age 25 to 35 and then stops can end up with more at 65 than someone who saves 200 a month from 35 to 65, because the early money has decades longer to grow. Try both in the calculator to see it for yourself.
Choosing a realistic return
Past returns don't guarantee future ones. Try a lower and a higher rate to see a range of outcomes, and remember that inflation and tax reduce real growth. This is a planning tool, not financial advice.
- Savings accounts and fixed deposits: usually low, around the current bank rate.
- Bonds: moderate, with less ups and downs than shares.
- Stock market index funds: historically higher over long periods, but with big swings from year to year.
Monthly contributions (SIP)
Regular monthly saving, often called a SIP (systematic investment plan) in India, adds steadily to your balance. The calculator adds your contribution every month and shows how much of the final amount is money you put in and how much came from growth. Saving and borrowing are two sides of the same maths: once you know what your savings can grow to, try the Loan Calculator to see what a loan would really cost. When a deal shows a rate as a plain figure, the Percentage Calculator and the Discount Calculator help you compare it with other offers.
Features
- Monthly contributions
- Yearly, quarterly, monthly or daily compounding
- Split between money in and interest earned
- Growth chart and yearly table
- Any currency
- Updates instantly
Frequently asked questions
What is compound interest?
It's interest calculated on your original money plus the interest it has already earned. Over time, your balance grows faster and faster, like a snowball.
What is the compound interest formula?
For a single deposit: A = P × (1 + r/n)^(n×t), where P is the starting amount, r the yearly rate, n how many times it compounds per year and t the number of years. With monthly contributions, each deposit grows the same way from the month it's added.
What return should I use?
Savings accounts typically pay a few percent a year. Broad stock market index funds have historically averaged around 7–10% a year before inflation, but returns vary a lot and aren't guaranteed.
Does compounding frequency matter much?
A little. Daily or monthly compounding earns slightly more than yearly at the same rate, but the rate, how much you save and how long you save matter far more.
Does this include taxes and inflation?
No. It shows growth before taxes, fees and inflation. To see results in today's money, subtract the expected inflation rate from your return.
How much will my savings grow?
Enter your starting amount, monthly contribution, expected yearly return and number of years. The final balance and the year-by-year table show your projected growth.
What is the rule of 72?
Divide 72 by the yearly return to estimate how many years it takes to double your money. At 8%, money doubles in about 9 years.
Is this financial advice?
No. It's a calculator for planning and learning. For decisions about your money, speak to a qualified financial adviser.