Compound Interest Calculator

How compound interest works

Compound interest is often called the eighth wonder of the world for a reason: your money earns returns, and then those returns earn returns of their own. The longer your money stays invested, the more dramatic the effect becomes — which is why starting early matters more than almost anything else.

This calculator lets you model a starting deposit, a recurring monthly contribution, an annual rate of return, a time horizon, and how often interest compounds. The chart above shows the widening gap between what you put in (contributions) and what you end up with (total balance) — that gap is the interest working for you.

What the numbers mean

• Future Value — your projected total balance at the end of the period.
• Total Contributions — every dollar you personally deposited.
• Total Interest Earned — the difference: growth from compounding.

Related articles

• How compound interest actually works — the formula, a worked example, and why the early years feel slow.
• The Rule of 72, explained — the mental-math shortcut for how fast your money doubles.
• How compounding frequency changes your returns — daily vs. monthly vs. yearly, and where it actually matters.

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Not financial advice. Results are estimates for educational purposes only. Real-world returns vary, are not guaranteed, and do not account for taxes, fees, or inflation.