Watch your money grow with compound interest
Compound interest is often called the eighth wonder of the world — and this free compound interest calculator shows you why. Enter a starting amount, a monthly contribution, an expected return and a time horizon, and see your future value, how much you actually put in, and how much of the total is pure interest earned. A year-by-year table makes the snowball effect impossible to miss.
It's perfect for planning savings goals, retirement, an emergency fund or any long-term investment. The calculator compounds monthly and grows every contribution, so the numbers reflect how real savings build up. Everything runs in your browser, free and private.
How to use it
- Choose your currency and enter your starting amount.
- Add a monthly contribution (use 0 for a lump sum only).
- Set your expected annual return and the number of years.
- Read your future value, total interest and the year-by-year growth.
What is compound interest?
Simple interest pays you only on your original money. Compound interest pays you on your original money and on all the interest you've already earned, so each period you earn interest on a bigger balance. Over a few years the difference is small; over decades it's enormous. That growing-on-growth is exactly what builds wealth from regular, patient saving.
The power of starting early
Because compounding accelerates, time is the most valuable ingredient — often more than the amount you invest. Someone who invests a modest sum for thirty years can end up well ahead of someone who invests far more but only for ten. Try it yourself: lengthen the years in the calculator and watch how the interest portion balloons compared with what you contributed.
Choosing a realistic rate
Your result is only as good as your assumed return. Savings accounts and fixed deposits typically pay a few percent. Broad, diversified stock-market investments have historically averaged around 7% a year after inflation over the long run, but returns swing widely year to year and the past doesn't guarantee the future. It's wise to run a cautious rate and an optimistic one to see the range.
Compound vs simple interest
Simple interest pays a fixed amount each period based only on your original deposit — put in 1,000 at 10% and you earn 100 every year, forever. Compound interest pays on the growing balance, so year two earns interest on 1,100, year three on 1,210, and so on. Over a year or two the gap is tiny, but over twenty or thirty years compound interest pulls dramatically ahead. This calculator uses monthly compounding, which is how most savings accounts and investment funds actually work, so the future value reflects real-world growth rather than the slower simple-interest figure.
Free, private and flexible
There's no signup and no limit, and the maths runs entirely on your device so your figures stay private. Switch currencies, change any input and the results update instantly. Remember this is a planning estimate, not financial advice — for decisions about real money, speak to a qualified adviser.