Compound Interest Calculator
The Compound Interest Calculator shows how an investment or deposit grows when interest earns interest over time. Enter your starting amount, the annual rate, the number of years and how often interest is compounded, and it reveals the final value and exactly how much of that is pure growth.
Why compounding is powerful
With simple interest you earn a return only on your original money. With compound interest you earn a return on your original money and on all the interest it has already earned. That second layer is small at first and enormous later, which is why starting early matters more than almost anything else in investing.
The formula
The future value is A = P × (1 + r/n)n·t, where P is the principal, r is the annual rate as a decimal, n is how many times a year interest is compounded, and t is the number of years. The interest earned is simply A − P.
A worked example
Invest 1,00,000 at 8% compounded monthly for 10 years. Here P = 100000, r = 0.08, n = 12, t = 10. The result is about 2,21,964, so your money more than doubles and about 1,21,964 of that is growth. Leave it for 20 years instead of 10 and it grows to roughly 4,92,680, far more than double the 10-year figure, because the later years compound on a much larger base.
The lever that matters most: time
Rate and contributions help, but time is the strongest multiplier. Try the same amount and rate over 5, 15 and 30 years here and watch the final value climb out of proportion to the extra years. More frequent compounding (monthly versus yearly) also helps, though the difference is smaller than most people expect.
How to use
- Enter your details in the fields above. The Compound Interest Calculator accepts everyday values and checks them as you type.
- Press the action button (or just start typing for live tools) to run the calculation.
- Read your result, along with any supporting figures, in the clearly labelled result box.
- Use Copy result to grab the answer, Reset to start again, or Copy link to share this tool.
Why use this tool
Finance Wave built the Compound Interest Calculator to be genuinely useful: it validates your input so you never see a broken result, formats numbers for your region automatically, and stays readable in both light and dark mode. Because everything happens on your device, it is private by design and keeps working even without an internet connection once the page has loaded.