What is compound interest?

Compound interest is interest earned on both your original principal and on previously earned interest. Unlike simple interest (calculated only on the principal), compound interest creates exponential growth over time because each period's interest becomes part of the next period's base.

How does compound frequency affect my returns?

More frequent compounding (daily vs. annually) means interest is calculated on a growing balance more often, resulting in slightly higher returns. The difference between monthly and daily compounding is small, but the difference between annual and monthly compounding can be meaningful over decades.

What is the Rule of 72?

The Rule of 72 is a quick mental math shortcut: divide 72 by your annual interest rate to estimate how many years it takes to double your money. At 7% returns, your money doubles roughly every 10.3 years. At 10%, every 7.2 years.

Why does time matter more than the amount invested?

Because compound interest is exponential, the longer your money compounds, the more dramatic the growth. Someone who invests $200/month starting at age 25 will have more at 65 than someone who invests $400/month starting at age 35, even though the late starter contributes more total dollars.

Should I use a tax-advantaged account?

Yes. Tax-advantaged accounts like 401(k)s, IRAs, and Roth IRAs let your investments compound without annual tax drag. In a taxable account, you lose a portion of gains each year to taxes, which reduces the compounding base. The W-2 Trap covers 7+ tax optimization strategies that can save W-2 earners thousands per year.

Compound Interest Calculator

See how your money grows exponentially when you let compound interest do the heavy lifting.

Starting Amount ($)

Annual Contribution ($)

IRA max: $7,000

Monthly Contribution ($)

Annual Interest Rate (%)

Compound Frequency

Investment Period (years)

Your Current Age

Annual Contribution Increase (%)

Increase contributions each year, e.g. 3% to match inflation

Tax Rate on Gains (%)

0 for 401k/IRA, 15 for long-term capital gains

Future Value

Total Contributions

Investment Gain

Gain % of Total

Balance Growth Over Time

Contributions Interest

Year 0 Year 30

The Doubling Milestones

Your money doubles every 10.3 years (Rule of 72)

First Double

Second Double

Third Double

Year-by-Year Breakdown

Year	Age	Annual Contrib.	Interest	Total Contrib.	Total Gain	Balance

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Disclaimer: This calculator provides estimates for educational purposes only. Actual returns vary. Inflation, taxes, fees, and market volatility will affect your real-world results. This is not financial advice. Consult a qualified financial planner.