How to use the Compound Interest Calculator
- Enter what you start with (it can be 0).
- Add how much you will contribute each month.
- Enter the yearly interest or expected return rate and the number of years.
- Choose how often interest compounds. The table shows your balance at the end of each year.
Formula used
With monthly contributions, each deposit is added at the end of the month and then compounds, as in most savings accounts and investment plans.
Interest earned = Final balance − Starting amount − Total contributionsWorked examples
| Start | Monthly | Rate | Years | Final balance |
|---|---|---|---|---|
| $10,000 | $0 | 10% | 10 | $27,070 |
| $0 | $500 | 7% | 30 | $609,985 |
| £5,000 | £200 | 5% | 10 | £39,292 |
| ₹1,00,000 | ₹0 | 8% | 5 | ₹1,48,985 |
The rule of 72
To estimate how long money takes to double, divide 72 by the yearly rate. At 8%, money doubles in about 9 years. Compare this with simple interest, where interest never earns interest. Investing monthly in mutual funds? Try the SIP Calculator.
Frequently asked questions
What is the difference between simple and compound interest?
Simple interest is paid only on the original amount. Compound interest is also paid on interest already earned, so growth speeds up over time.
Does compounding frequency matter much?
A little. At 10% for 10 years, monthly compounding gives about 2.7% more than yearly. The rate and the time invested matter far more.
Can I use this for a 401(k), ISA or index fund?
Yes, as an estimate. Enter your expected yearly return. Real investment returns vary and are not guaranteed.
Does this include tax or inflation?
No. To see real growth, subtract inflation from your return rate. Tax-free accounts such as ISAs and Roth IRAs avoid tax on growth.
What is the formula in Excel?
Use =FV(rate/12, years*12, -monthly, -start). For example =FV(10%/12, 120, 0, -10000) returns about 27,070.
Our team builds and tests every tool by hand, checks each formula against official sources (IRS, HMRC, the Income Tax Department of India, CBSE, NHS, WHO) and reviews pages whenever rules change. Last reviewed on . Spotted a mistake? Tell us.