Compound Interest Calculator

See how savings and investments grow over time with compound interest and regular contributions, including a visual growth chart. Free, instant, private.

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Final value
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Total contributions
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Interest earned
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This calculator provides general information only and is not financial advice. Actual returns vary and are not guaranteed; it assumes a constant rate and does not account for taxes, fees or inflation. Consult a qualified financial professional before making investment decisions.

How to use the Compound Interest Calculator

  1. Enter your starting principal and any regular monthly contribution.
  2. Enter the annual interest rate and choose how often interest compounds.
  3. Enter the number of years to project.
  4. Read the final value, total contributions and interest earned, and watch the growth chart update live.

Why use ZillaKit's Compound Interest Calculator?

Compound interest is the effect of earning interest not just on your original money but on the interest it has already earned, and over long periods it is the single biggest driver of investment growth. This calculator lets you combine a starting principal with steady monthly contributions, then projects the balance forward at your chosen rate and compounding frequency. It separates the total you put in from the interest that money generated, so you can see clearly how much of the final figure is your own contributions versus growth. The chart draws two lines — one for cumulative contributions and one for total value — so the widening gap between them makes the power of compounding visible at a glance. The colours adapt to whichever theme you are using. Everything recalculates instantly as you adjust any input, which makes it easy to test how a higher contribution, a longer horizon or a different rate changes the outcome. All maths runs locally in your browser with plain JavaScript, so there is no upload, no signup and nothing stored. The results are illustrative projections for planning, not a guarantee or financial advice.

FAQ

How is compound interest calculated?

The balance grows each compounding period by the periodic rate, which is the annual rate divided by the number of periods per year. Contributions are added along the way and then also earn interest, which is why more frequent compounding and longer time horizons produce larger totals.

Does compounding frequency really matter?

Yes, though the effect is modest at typical rates. Daily compounding yields slightly more than annual compounding for the same nominal rate, because interest is added and starts earning sooner.

Does this account for inflation, taxes or fees?

No. The projection uses your nominal rate only. Real purchasing power, taxes and investment fees would reduce the effective outcome, so treat the figures as a before-costs illustration.

Is my data uploaded anywhere?

No. All calculations run in your browser using JavaScript. Nothing you enter is sent to a server or stored.