Investment Compound Interest Calculator
Project how an investment grows with compound interest, plus optional recurring monthly contributions, with a visual year-by-year growth chart.
This calculator provides estimates only and is not financial advice. Consult a qualified financial advisor for personalized guidance.
How to use this calculator
Enter your starting principal, annual interest rate, compounding frequency, and time period. Optionally add a monthly contribution to see how regular investing accelerates growth, then click Calculate Growth. The chart shows how much of your final balance came from contributions versus interest earned each year.
How is this calculated?
With no monthly contribution, this uses the standard compound interest formula A = P × (1 + r/n)^(n×t), where A is the final balance, P is the principal, r is the annual interest rate, n is the number of times interest compounds per year, and t is the number of years. With a monthly contribution, the calculator instead simulates growth month by month so each contribution compounds alongside your principal for the remaining time period.
Worked example: $10,000 plus $200 a month
With the default inputs ($10,000 to start, $200 added every month, 7% a year compounded monthly, 20 years), the balance reaches $144,572.72. You put in $58,000 ($10,000 plus 240 contributions of $200), and the other $86,572.72 is growth. Without the monthly contributions, the same $10,000 grows to $40,387.39, so the habit of adding money matters more here than the starting amount.
Compounding frequency vs. rate and fees
Changing only how often interest compounds moves the 20-year result surprisingly little: with the calculator's three options, yearly compounding gives $140,204.12, quarterly $143,739.17 and monthly $144,572.72. The rate matters far more. Taking one point off the return, from 7% to 6% (roughly the drag of a 1% annual fund fee), ends at $125,510.22, about $19,000 less. Check the expense ratio of a fund before worrying about compounding frequency.
The projection assumes the same return every year and adds each contribution at the end of the month. Real markets move unevenly, and the result is in future dollars, before taxes and inflation. Treat it as a planning range, not a promise.
For a single deposit, or an amount in rupees
This calculator is built for investing in dollars with regular monthly additions and a year-by-year growth chart. For a single deposit, such as a fixed deposit, set the monthly contribution to 0: the result is then plain compound interest on the starting amount. The arithmetic is the same in any currency, so a rupee amount works too; read the dollar sign as a rupee sign. To see how compounding compares with simple interest on the same amount, read simple vs compound interest.
Frequently Asked Questions
What is compound interest?
Compound interest is interest earned on both your original principal and on the interest that has already accumulated. Over time this creates exponential rather than linear growth, since each period's interest is calculated on a larger balance than the last.
How often should interest compound?
More frequent compounding (monthly vs. annually) produces slightly higher returns for the same nominal interest rate, because interest starts earning interest sooner. The difference is usually small compared to the impact of the interest rate itself or regular contributions.
How much difference do monthly contributions make?
Regular contributions can dramatically increase your final balance, since each new contribution has years to compound. Try setting the monthly contribution field to 0 and comparing the result to a nonzero value to see the effect for your own numbers.
What's a realistic rate of return to use?
There is no safe single number. Returns vary from year to year, are never guaranteed, and fund fees come straight off them. Run the calculator at the rate you expect and at one or two points below it, and plan around the lower results.