Use this free compound interest calculator to see how savings and investments grow when interest earns interest. Enter your starting amount, rate and years, choose how often interest is compounded, and watch the growth.
What Is the Compound Interest Calculator?
Compound interest is interest calculated on your starting amount plus all the interest already earned, so your money grows faster over time than with simple interest. Each time interest is added, the next calculation is based on a larger amount. This is how savings accounts, fixed deposits and long-term investments grow. The longer money is left invested, and the more often interest is compounded, the stronger the growth effect becomes over the years.
How to Use This Calculator
- Enter your starting amount.
- Enter the annual interest rate.
- Enter the number of years.
- Choose how often interest is compounded.
- Click Calculate Growth.
Formula
A = P × (1 + r ÷ n)^(n × t), where A = future value, P = principal, r = annual rate as a decimal, n = compounding periods per year, t = years.
Worked Example
10,000 at 8% per year for 10 years, compounded annually, grows to 21,589.25 — interest of 11,589.25. Compounded monthly instead, the same money grows to 22,196.40.
How It Works, In Plain Words
Read the formula as a machine with four dials. P is the principal, the 10,000 you start with. r is the annual rate turned into a decimal — the 8% you type becomes 0.08 inside the formula — and n is how many times a year interest is added: 1 for annually, 4 quarterly, 12 monthly, 365 daily, exactly the choices in the Compounded menu. t is the years, 10 in the example. The engine room is the bracket, (1 + r ÷ n): each compounding period grows the pot by that share of itself, annually by the full 8% at once. The power, (n × t), says how many times that growth is applied — 10 times for the annual example, 120 times for monthly. Because each application works on a pot that already includes earlier interest, growth accelerates: the example’s interest alone, 11,589.25, ends up larger than the 10,000 principal. The tool then splits the answer into the two lines you see: the future value, and the interest earned, which is simply the future value minus what you put in.
Real-World Uses
First scenario: a fixed deposit decision. The saver has 10,000 and a 10-year horizon, and the deposit in front of them matches the worked example — 8%, compounded annually, 21,589.25 at the end. Seeing the interest line, 11,589.25, come out larger than the deposit itself makes the long term feel worth committing to. Second: comparing two accounts that quote the same 8% but compound differently. Switching the menu to Monthly shows 22,196.40 — the page’s own comparison — a difference of 607.15 earned purely from more frequent compounding, with no extra money paid in. Third: setting a savings goal. The Benefits list points at realistic goals, and the practical method is to work backwards: try principals and year counts until the future value meets the target, then judge whether those inputs are achievable. In all three, the rate is an input to test, never a promise — the mistakes list is blunt that a past rate of return does not repeat exactly.
Benefits
- See why starting early matters more than saving more later.
- Compare compounding frequencies.
- Set realistic savings goals.
- Understand investment growth before committing money.
Features of Our Tool
- Instant results as you click Calculate — no page reload
- Shows the full breakdown, not just one number
- Free forever, no sign-up or download
- Works on phones, tablets and computers
- Your numbers stay in your browser — nothing is stored
Common Mistakes to Avoid
- Using simple interest maths for long periods.
- Forgetting inflation reduces real growth.
- Assuming a past rate of return will repeat exactly.
More Common Mistakes to Avoid
The rate box causes more quiet errors than any other. It takes the annual figure — type 8 for 8% — so entering a monthly rate, or 0.08 because the formula shows r as a decimal, shrinks or explodes the result while looking perfectly reasonable; the decimal conversion happens inside the tool. Second, this calculator grows a single lump sum: there is no box for regular additions, so typing a savings plan’s total contributions as the principal overstates the growth, because that money was not invested from day one. Third, mind the Compounded menu — leaving it on Annually when your account compounds monthly understates the result by the page’s own comparison, 21,589.25 against 22,196.40. And keep the mistakes list’s warnings in view while you plan: simple-interest maths understates long horizons, and the future value is stated in tomorrow’s money, before inflation has had its say.
Frequently Asked Questions
What is compound interest?
Compound interest is interest earned on both the original amount and on interest already earned, so your money grows faster over time.
How often is interest compounded?
Common schedules are annually, quarterly, monthly and daily. The more often interest compounds, the slightly higher the final amount.
What is the difference between simple and compound interest?
Simple interest is paid only on the original principal. Compound interest is paid on principal plus accumulated interest.
How much will 10,000 grow to at 8% in 10 years?
At 8% compounded annually, 10,000 grows to 21,589.25 in 10 years.
Does compounding frequency change the result much?
Over long periods yes: the same 10,000 at 8% for 10 years reaches 22,196.40 with monthly compounding versus 21,589.25 annually.
Why is the interest earned more than I deposited?
Because of the compounding itself. In the worked example the interest, 11,589.25, passes the 10,000 principal because each year’s interest joins the pot and earns interest of its own for the years that remain. Given enough time that snowball is the whole point of compounding — and why the Benefits list says starting early matters more than saving more later.
Does this calculator include regular monthly deposits?
No. It grows one starting amount — the principal — over the years you enter, with nothing added along the way. If you save in regular instalments, this tool still shows what a single lump sum would do, but a plan built on regular contributions needs a calculator designed for that pattern; the SIP Calculator in the Related list below is this site’s tool for it.