💹 Compound Interest Calculator
See exactly how your money grows when interest earns interest. Add monthly contributions, choose any compounding frequency, and get your final balance, total interest, APY, doubling time and a year-by-year growth chart — instantly, in any currency. Free & private.
* Estimates only, assuming a steady rate and end-of-month contributions. Real returns vary. Not financial advice.
Key Insights — tap any card for details
🔁 How Compounding Frequency Changes Your Result
Same 8% rate, same 15 years — only the compounding frequency changes. Notice how the gains shrink as frequency rises toward the continuous ceiling.
📊 Year-by-Year Breakdown
| Year | Invested | Interest (year) | Total Interest | Balance |
|---|---|---|---|---|
| Year 1 | $16,000 | +$1,055 | $1,055 | $17,055 |
| Year 2 | $22,000 | +$1,641 | $2,695 | $24,695 |
| Year 3 | $28,000 | +$2,275 | $4,970 | $32,970 |
| Year 4 | $34,000 | +$2,961 | $7,932 | $41,932 |
| Year 5 | $40,000 | +$3,705 | $11,637 | $51,637 |
| Year 6 | $46,000 | +$4,511 | $16,148 | $62,148 |
| Year 7 | $52,000 | +$5,383 | $21,531 | $73,531 |
| Year 8 | $58,000 | +$6,328 | $27,859 | $85,859 |
| Year 9 | $64,000 | +$7,351 | $35,210 | $99,210 |
| Year 10 | $70,000 | +$8,459 | $43,669 | $113,669 |
| Year 11 | $76,000 | +$9,659 | $53,329 | $129,329 |
| Year 12 | $82,000 | +$10,959 | $64,288 | $146,288 |
| Year 13 | $88,000 | +$12,367 | $76,655 | $164,655 |
| Year 14 | $94,000 | +$13,891 | $90,546 | $184,546 |
| Year 15 | $100,000 | +$15,542 | $106,088 | $206,088 |
What Is Compound Interest?
Compound interest is interest you earn on your interest. With simple interest, only your original deposit ever earns — so $1,000 at 10% pays a flat $100 every year, forever. With compound interest, each year's interest joins your balance and starts earning too: $100 the first year, $110 the next, $121 after that, and so on. That tiny shift — paying interest on interest — is what turns steady saving into serious wealth, and why Albert Einstein is often quoted (probably apocryphally) calling it the eighth wonder of the world. The same force works in reverse on debt, which is why credit-card balances spiral. This calculator shows the upside: feed in a rate and a time period and watch the curve bend upward.
Any Compounding Frequency
Daily, monthly, quarterly, yearly or continuous — and a panel that compares them side by side for your numbers.
Monthly Contributions
Model regular deposits on top of your starting amount, the way real savings plans and retirement accounts work.
Growth Chart & Breakdown
Watch the gap between money-in and balance widen on an interactive chart, with a full year-by-year table.
APY, Rule of 72 & More
See your effective annual yield, doubling time, money multiplier and the exact 'interest on interest' bonus.
Multi-Currency
Switch between dollars, rupees, euros, pounds, yen and more — useful anywhere in the world.
Free, Private & Mobile
No sign-up, nothing uploaded, full dark mode, and responsive down to 280px phone screens.
The Compound Interest Formula
The classic formula is A = P(1 + r/n)nt, where A is the final amount, P is your principal (starting amount), r is the annual interest rate as a decimal, n is how many times interest compounds per year, and t is the number of years. The more often it compounds (a bigger n), the larger A becomes — and as n heads toward infinity you reach continuous compounding, A = Pert. When you add regular deposits, this tool also sums the future value of every contribution, so the figure you see reflects both your lump sum and your ongoing saving.
How to Use the Compound Interest Calculator
Four quick steps — every number updates the instant you change a slider.
Enter your starting amount
Set your principal and, if you like, a monthly contribution. Click any value to type an exact number.
Set rate & compounding
Choose your annual interest rate and how often it compounds — daily, monthly, quarterly, yearly or continuous.
Pick a time period
Drag the years slider and watch your final balance, interest and chart update instantly.
Explore the insights
Tap the insight cards for APY, the Rule of 72 and the compounding bonus, and scan the year-by-year breakdown.
Frequently Asked Questions
What is compound interest?
Compound interest is interest earned on both your original money and on the interest it has already earned. Unlike simple interest, which only ever pays on the starting amount, compound interest pays interest on interest — so your balance grows faster and faster over time. It's the single most important idea in personal finance, working for you when you invest and against you when you borrow.
How does this compound interest calculator work?
Enter your starting amount, an optional monthly contribution, the annual interest rate, how often interest compounds (daily, monthly, quarterly, yearly or continuously) and the number of years. The calculator instantly shows your final balance, the total interest earned, your effective annual yield (APY), how long your money takes to double, and a year-by-year growth chart. Every number updates the moment you move a slider.
What is the compound interest formula?
The standard formula is A = P(1 + r/n)^(nt), where A is the final amount, 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, and t is the number of years. For continuous compounding it becomes A = Pe^(rt). When you add regular contributions, the calculator also adds the future value of those deposits on top.
Does compounding frequency really make a difference?
Yes, but with diminishing returns. Compounding monthly earns noticeably more than compounding once a year at the same rate, and daily earns a little more still. However, the gains shrink as frequency rises — the jump from annual to monthly is large, while the step from daily to 'continuous' compounding is tiny. The calculator's comparison panel shows the exact difference for your numbers.
What is APY and how is it different from the interest rate?
APY (Annual Percentage Yield), also called AER or the effective annual rate, is the true yearly return once compounding is included. A 'nominal' 12% rate compounded monthly actually yields about 12.68% a year. Because two accounts with the same headline rate can pay different amounts depending on how often they compound, APY is the honest, comparable figure — always compare savings accounts by APY, not the nominal rate.
What is the Rule of 72?
The Rule of 72 is a quick mental shortcut for how long money takes to double: just divide 72 by the interest rate. At 8%, money doubles in roughly 72 ÷ 8 = 9 years. It's surprisingly accurate for rates between about 4% and 12%, and it's a centuries-old trick that lets you estimate compounding in your head without a calculator.
Should contributions be added monthly or yearly?
This calculator adds your contribution every month at the end of the month, which matches how most people save into a retirement account, savings plan or SIP. Contributing monthly rather than once a year means more of your money is invested earlier, so it has more time to compound — a small but real advantage over the long run.
Is the compound interest calculator free and private?
Completely free, with no sign-up and no limits. Every calculation runs entirely in your browser — none of your numbers are sent to a server or stored anywhere. You can switch between US dollars, rupees, euros, pounds, yen and more, and it works on any device down to very small phone screens.