📈 Compound Interest Calculator

The Compound Interest Calculator shows how a starting balance grows over time when interest is earned on both the original amount and previously-earned interest — optionally with regular monthly contributions. It is the clearest way to see why starting early matters so much for savings and investments.

How to Use This Tool

Enter the starting amount, the annual interest rate, the number of years, how often interest compounds, and an optional monthly contribution. The tool shows the final balance, the total you contributed, and the interest earned.

What This Tool Checks

Compound growth of the principal — A = P(1 + r/n)^(nt) — plus the future value of a monthly contribution stream compounded at the same rate. All figures are computed exactly in the browser.

Understanding Your Results

The final balance is what you would have at the end. "Total contributed" is your own money in; "interest earned" is everything above that — the part compounding creates for you. On long horizons the interest often dwarfs the contributions.

How to Fix Common Problems

If growth looks too small, check the rate is annual and the years are correct. More frequent compounding (monthly vs annually) increases the result slightly, but the rate and time horizon matter far more than the compounding frequency.

SEO Best Practices

Use a realistic long-run rate rather than a single good year. Remember this is a pre-tax, pre-inflation projection — real returns are lower after both. It is a planning illustration, not a guaranteed forecast, and not investment advice.

Example

$1,000 at 6% compounded monthly for 10 years grows to about $1,819 with no contributions. Add $100 a month and the balance passes $17,000 — of which roughly $13,000 is contributions and the rest is compound interest.

Common Mistakes to Avoid

Assuming a single year's return will repeat every year overstates growth. Ignoring inflation and tax makes the future balance look more valuable in today's money than it really is.