Wealth & Investing

Compound Interest Calculator

Discover how your money can grow over time. Calculate the future value of your investments with the power of compounding.

Visual Growth Curve
Investment Tracking
Monthly vs Annual
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Wealth Tool

Interactive Growth Calculator

Estimate the future value of your portfolio for 2026 and beyond.

Updated for 2026⚡ Instant Results

Growth Engine

Investment Details

The S&P 500 has historically returned an average of about 10% annually before inflation (or 7-8% adjusted for inflation).

Future Portfolio Value

$345,742

Total Principal

$130,000

Interest Earned

+$215,742

In year 20, your money earns $26,284 in interest alone! This is the power of compounding.

All calculations run locally in your browser • No data stored • For estimation purposes only

Investing Rules of Thumb

10%

S&P 500 Average

Historical annual return

Rule of 72

Doubling Time

72 / rate = years to double

Time

The Secret Weapon

Start as early as possible

Taxes

Erode Returns

Use Roth IRAs to avoid them

The Power of Compound Interest

Albert Einstein called it the 8th wonder of the world.

"Compound interest is the eighth wonder of the world. He who understands it, earns it... he who doesn't... pays it." Whether Einstein actually said this or not, the math holds true. It is the single most important concept in personal finance.

How Does It Work?

Imagine you invest $10,000 and it grows by 10% in the first year. You now have $11,000. In year two, if it grows by 10% again, you don't just earn another $1,000. You earn 10% on the new balance of $11,000, giving you $1,100 in interest.

This snowball effect continues. By year 30, that same 10% growth isn't generating $1,000 a year—it's generating $15,000+ a year in pure interest, without you lifting a finger.

  • Start Early: Time is more important than money in compounding.
  • Be Consistent: Automate your monthly contributions.
  • Reinvest: Never withdraw the dividends; reinvest them.
  • Avoid Fees: High expense ratios eat your compound growth.

The Danger of Debt

Compound interest works both ways. When you carry a balance on a credit card, the credit card company is compounding interest against you. This is why credit card debt is so hard to escape. Always pay off high-interest debt before investing!

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FAQ

Wealth & Investing Questions

What is Compound Interest?
Compound interest is the interest on savings calculated on both the initial principal and the accumulated interest from previous periods. Put simply, it's 'interest on interest,' and it is the most powerful force in building long-term wealth.
What is the Rule of 72?
The Rule of 72 is a quick mental math trick to determine how long an investment will take to double. You simply divide 72 by your expected annual rate of return. For example, at an 8% return, your money will double every 9 years (72 / 8 = 9).
What is a realistic rate of return?
Historically, the S&P 500 (the 500 largest US companies) has returned an average of about 10% annually before inflation. Adjusting for inflation, a realistic long-term rate of return for a stock-heavy portfolio is typically estimated between 7% and 8%.
Does contribution frequency matter?
Yes! Contributing monthly rather than annually puts your money into the market faster, allowing it to start compounding sooner. Over a 30-year period, contributing $500 monthly will result in significantly more wealth than contributing $6,000 once a year.