How Compound Interest Works

Maintained by Prince Yadav — Founder & Lead Developer, Ganitra Calculator. This guide is written and maintained as part of Ganitra Calculator’s first-party educational content.

What is compounding?

Compound interest earns returns on the original principal and on accumulated interest from earlier periods.

The formula

A = P(1 + r/n)^(nt). The result depends on the starting amount, rate, compounding frequency, and time.

Why time matters

Because growth compounds, a longer time horizon can have a large effect on the final value even when the rate stays the same.

Compounding frequency

The same nominal annual rate can produce different results depending on how often interest is added. Compare monthly, quarterly, and annual assumptions consistently.

Contributions change the picture

Regular contributions can accelerate growth because new money also has time to compound. The result remains a projection based on the chosen assumptions.

Worked example

If a starting balance earns a steady assumed rate for several years, the balance grows each period and the next period begins from that larger base.

Nominal versus real growth

A projected balance is not the same as purchasing power. Inflation, taxes, fees, and changing returns can reduce the real-world outcome.

Using the calculator

Test the same starting amount with different rates, frequencies, and time periods. The comparison is more useful than treating one projection as guaranteed.

Related Calculators

Use the Calculator

Take the concepts from this guide and test your own assumptions in the calculator.