Compound Interest Calculator

📈 Compound Interest Calculator

Principal ($)

Annual Rate (%)

Years

Compound Frequency

Monthly Contribution ($)

What is the Compound Interest Calculator?

This calculator projects how a lump-sum investment grows over time when interest is earned not just on your principal but on previously earned interest too. Enter a starting principal, annual rate, time horizon, compounding frequency, and an optional monthly contribution, and it computes your final balance, total amount contributed, total interest earned, and what share of the final balance came from interest versus your own deposits.

How to Use It

Fill in the principal, annual interest rate, number of years, how often interest compounds (daily, monthly, quarterly, semi-annually, or annually), and any monthly contribution you plan to add. Click Calculate to see the results and a year-by-year growth chart comparing your total balance against your total contributions.

When to Use It

Use it to project retirement or brokerage account growth, to see how a high-yield savings account compares to a lower-rate one over years, or to test how adding a monthly contribution changes your outcome versus a one-time deposit. It's also useful for comparing compounding frequencies side by side.

Who Benefits

Anyone planning long-term savings — new investors deciding how much to contribute monthly, parents saving for a child's education, and workers estimating retirement account growth — can use it to see the real impact of time and compounding frequency before committing money.

Frequently Asked Questions

The more often interest is added to your balance, the sooner it starts earning interest on itself. Daily compounding produces a slightly higher final balance than monthly, which is slightly higher than annual, at the same stated rate — the gap widens the longer your money stays invested.

It shows what percentage of your final balance came from interest rather than your own contributions. A high ratio means compounding did most of the work; a low ratio means most of your balance is money you personally deposited.

Contributions are added at the end of each month, right after that month's interest is applied to the existing balance, which matches how most savings and brokerage accounts handle recurring deposits.

📈 Compound Interest Calculator