Compound Interest Calculator

Calculate Your Investment Growth

Free Compound Interest Calculator

Use this free compound interest calculator to see exactly how your savings and investments grow over time. Enter a starting balance, an interest rate, and optional monthly contributions, and the tool projects your future value year by year with an interactive chart. Whether you are planning for retirement, building an emergency fund, comparing a high-yield savings account against an index fund, or running a "what if" on a one-time deposit, you get accurate numbers in seconds — and every calculation runs entirely in your browser.

Unlike a simple savings calculator, this one models regular contributions, compounding frequency (daily, monthly, quarterly, or annually), inflation, and tax on interest — so the projection reflects what you would realistically keep, not just a headline number.

How to Use the Calculator

1. Enter your initial investment (starting principal).
2. Set the annual interest rate and how often interest compounds.
3. Add a regular contribution — monthly, bi-weekly, weekly, or annually.
4. Optionally expand Advanced Options to adjust for inflation and tax.
5. Click Calculate to see your projected growth, chart, and year-by-year table.

The Compound Interest Formula

Compound interest is calculated with the formula A = P(1 + r/n)^nt, where:

• A — the future value (your final balance)
• P — the principal (your starting amount)
• r — the annual interest rate as a decimal (7% = 0.07)
• n — how many times interest compounds per year
• t — the number of years

When you add regular deposits, each contribution earns compound interest from the moment it lands, so the calculator sums the growth of your principal and every future deposit. To learn how this differs from a flat interest rate, read our guide on compound vs. simple interest.

A Worked Example

Say you invest $10,000 at a 7% annual return, compounded monthly, and add $200 every month for 30 years. You would contribute $82,000 of your own money, but end with roughly $320,000 — meaning compound interest earned you about $228,000 on top of what you put in. Push the timeline to 40 years and the same plan clears half a million dollars. That widening gap between contributions and interest is the snowball effect in action, and it is why starting early matters more than picking the perfect rate.

Common Use Cases

• Retirement planning — project a 401(k), IRA, or pension pot over decades.
• Savings goals — work out how long it takes to reach a house deposit or college fund.
• Comparing accounts — pit a high-yield savings APY against an index-fund return.
• Debt awareness — see how the same math works against you on a credit-card balance.
• FIRE planning — model aggressive contributions toward financial independence.

Features

• Regular contributions — Model monthly, weekly, or annual deposits
• Inflation adjustment — See your returns in real purchasing power
• Tax impact — Factor in tax rates on interest income
• Interactive chart — Visualize growth of principal vs. interest
• Year-by-year breakdown — Detailed table of balances over time
• Export results — Download as CSV or JSON
• Client-side calculations — Inputs and results stay in your browser

The Power of Compound Interest

Compound interest is often described as interest earning interest. Starting early and contributing regularly are two powerful factors because each period's gains can become part of the balance used for future growth. A fast way to feel the effect is the Rule of 72: divide 72 by your rate to estimate how many years it takes your money to double. For a deeper walkthrough of the mechanics, see how compound interest works.

Browse all of our compound interest guides for more strategies and worked examples.