Kalkulo / Money & Loans / Compound Interest Calculator

Compound Interest Calculator

See how a starting balance and fixed monthly deposits grow over time with compound interest.

Final balance
$17,175
after 10 years
Total deposited
$13,000
Interest earned
$4,175

How to use the compound interest calculator

  1. Enter the starting balance you have today (0 if starting from scratch).
  2. Enter how much you save per month, and the expected annual interest rate.
  3. Enter how many years you plan to save.

How compound interest is calculated

Final balance = Starting balance × (1 + r)n + Monthly deposit × ((1 + r)n − 1) ÷ r
where r is the monthly interest rate (annual rate ÷ 12 ÷ 100), and n is the number of months.

Compound interest means you earn interest on the interest you've already earned, not just on the original amount — that's why savings grow faster and faster the longer you wait. The effect is largest when the time horizon is long, even with a modest monthly amount.

Note: This is a projection based on a fixed, assumed interest rate — actual returns on stocks/funds fluctuate year to year and can be both higher and lower than assumed. Savings accounts typically have lower, but more predictable, interest.

Frequently asked questions

What's the difference between interest and compound interest?

Interest is the return on the original amount. Compound interest is when the interest you've already earned starts earning its own return — your money "works" for you at an ever-increasing pace, even if you don't add more.

Why is a long time horizon so important?

Because the compounding effect is exponential, not linear — the last years of a long savings period often contribute more growth than the first, even if you save exactly the same amount every month. Starting early gives the effect more time to work.

What interest rate should I use?

For a regular savings account, use the rate your bank quotes directly. For stocks/funds there's no guaranteed rate — many use a historical average (e.g. 5–7% for global stock funds over the long run) as a cautious estimate, not a guarantee.