Compound Interest Calculator
Calculate compound growth over time from principal, rate, and duration.
Written by Anil Gautam · Updated
What formula does the compound interest calculator use?
It compounds once a year: final amount = P × (1 + r/100)^t, where P is the principal, r the annual rate in percent and t the number of years. Results are rounded to the nearest rupee, so ₹1,00,000 at 8% for 5 years shows ₹1,46,933, with ₹46,933 of interest.
Each year's interest joins the balance, so the yearly amount grows: ₹8,000 in year one, then ₹8,640, ₹9,331, ₹10,078 and ₹10,884. Simple interest on the same deposit would total ₹40,000, which means ₹6,933 of the result is interest earned on earlier interest.
Type the rate as a percentage, 8 for 8%. Entering 0.08 is read as 0.08% and gives ₹1,00,401 after 5 years, so a result barely above the principal points to a rate typed as a fraction.
How long does it take money to double?
The rule of 72 gives a quick estimate: divide 72 by the annual rate. At 8% that is 9 years, and the calculator agrees, turning ₹1,00,000 into ₹1,99,900 after 9 years. For 12% the rule says 6 years, and the calculator shows ₹1,97,382.
Time matters as much as rate. At 8%, ₹1,00,000 earns ₹1,15,892 of interest in 10 years and ₹3,66,096 in 20, so doubling the period more than triples the interest.
The same formula projects rising prices. At 6% inflation a year, something that costs ₹1,00,000 today costs about ₹1,79,085 after 10 years. Dividing the 10-year result at 8%, ₹2,15,892, by that figure gives about 1.21, so the money buys roughly 21% more than it did at the start.
When should you use a different calculator?
This tool has one compounding period per year and no regular contributions. Indian bank fixed deposits usually compound quarterly, so FD Calculator fits them better: ₹1,00,000 at 8% compounded quarterly for 5 years gives ₹1,48,595, compared with ₹1,46,933 here. For a fixed monthly investment, use SIP Calculator. A recurring bank deposit belongs in RD Calculator, and loan repayments in EMI Calculator.
A rate that changes partway through can still be handled in steps. Run 3 years at 8% to get ₹1,25,971, then enter that amount as the principal for 2 more years at 7%, which gives ₹1,44,224.