Estimate how a monthly SIP, optional step-up and starting lump sum could grow over time.
Compound Interest Calculator
See how an investment grows with compound interest over time, with optional regular contributions.
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Future value
Total contributed
Total interest earned
Year-by-year growth
| Year | Total contributed | Interest | Balance |
|---|
This is a mathematical illustration. Real returns vary. Your numbers are calculated in your browser and are not sent to our server.
Runs entirely in your browser. Your files and text are not uploaded.
How to use Compound Interest Calculator
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Step 1: Enter the starting amount
Type the principal — the money you start with.
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Step 2: Set rate and period
Enter the annual interest rate, how many years you plan to invest, and how often interest compounds.
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Step 3: Read the result
The future value, total interest and a year-by-year table update as you type. Add a monthly contribution to see its effect.
The compound interest formula
A = P × (1 + r/n)^(n×t)
- A is the future value (principal + interest).
- P is the principal (starting amount).
- r is the annual interest rate as a decimal.
- n is the number of times interest compounds per year (1 for yearly, 4 for quarterly, 12 for monthly, 365 for daily).
- t is the number of years.
With regular contributions
When you add a fixed amount each compounding period, the future value of those contributions is:
FV = C × ((1 + r/n)^(n×t) − 1) / (r/n)
The total future value is the sum of the compounded principal and the compounded contributions.
Why compounding matters
Compound interest earns interest on the interest already added. Over long periods this "interest on interest" effect can be dramatic. The longer the time and the more frequent the compounding, the greater the effect.
Simple vs compound interest
Simple interest is charged only on the original principal: I = P × r × t. It grows in a straight line. Compound interest grows as a curve, because each period's interest is added to the principal before the next period's interest is calculated.
Limitations
- The interest rate is assumed to stay the same for the entire period.
- Taxes, fees and inflation are not included.
- Contributions are assumed to be made at the end of each compounding period.
- Very high rates or long periods may produce numbers that look unrealistic; the result is mathematically correct but real investments are never guaranteed.
- Your numbers are not saved or sent anywhere.
Frequently asked questions
What is compound interest?
Compound interest is interest calculated on the initial principal and also on the accumulated interest from previous periods. It makes your money grow faster than simple interest.
How often should interest compound?
More frequent compounding (monthly or daily) gives a slightly higher return than yearly compounding at the same rate, because interest is added to the principal sooner.
Can I add monthly contributions?
Yes. Enter a regular contribution amount and the calculator will show how the additional deposits grow alongside your principal.
Is this an investment forecast?
No. It is a mathematical illustration. Real investment returns vary and are not guaranteed.
What is the difference between APR and APY?
APR is the stated annual rate. APY (annual percentage yield) accounts for compounding. This calculator takes the APR and applies the compounding frequency you choose to show the effective growth.
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