Compound Interest Calculator

Home
Calculators
Compound Interest

What is "Compound Interest"?

Compound interest is when interest is calculated on both the initial principal and the accumulated interest from previous periods. This 'interest on interest' causes exponential growth over time. Albert Einstein reportedly called it the 'eighth wonder of the world' due to its powerful wealth-building effect.

Example: $10,000 at 7% compound interest for 30 years → $76,000 (7.6x the principal)

Initial Investment$10,000.00

Monthly Deposit$500.00

Annual Interest Rate (%)

0%10%20%

Investment Period (Years)

1y25y50y

Last Year Rate Assumption (%)

Used for the "this year vs last year" simulation.

Compound FrequencyResults update in real time when you move the rate/term sliders.

Total Invested

$130,000.00

$130.0K

Total Interest Earned

+$170.9K

Final Amount 🚀

($300.9K)

Growth Chart

You vs Average

Benchmark: U.S. long-term average return assumed at 7%

Final gap: +$0.00

This Year vs Last Year

Compares one-year outcomes using current and last-year return assumptions.

End-of-year difference: +$134.00

💰

Compound Interest Result

$300,851.00

✨ Estimated interest: $170,851.00

Expected value after 20 years (7% annual return)

📢 Share with friends

Share this useful information

#CompoundInterest #Investment #Finance #WealthBuilding

💸What if I keep this for retirement?

👉 Calculate my retirement asset and monthly pension

What is Compound Interest?

Compound interest is interest calculated on both the initial principal and the accumulated interest from previous periods. Unlike simple interest, which is calculated only on the principal amount, compound interest allows your money to grow faster over time.

The Compound Interest Formula

A = P(1 + r/n)^nt

A = P(1 + r/n)^(nt) where A is the final amount, P is the principal, r is the annual interest rate, n is the number of times interest is compounded per year, and t is the time in years.

The Rule of 72

The Rule of 72 is a simple way to estimate how long it will take for an investment to double. Divide 72 by your annual rate of return to get the approximate number of years. For example, at 6% annual return, your investment will double in about 72÷6=12 years.

At 7% return, your investment doubles in about 10.3 years.

How to Read the Comparison Features

"You vs Average": See whether your assumptions outperform or underperform a U.S. long-term baseline.
"This Year vs Last Year": Quantify how a rate change shifts your one-year ending value under the same contribution plan.
Rate and term sliders update charts in real time so you can test scenarios quickly.

Compound Interest Tips

✓Start investing early to maximize compound growth
✓Make regular contributions, even small amounts add up
✓Reinvest your earnings to accelerate growth
✓Think long-term for the best results

Last updated: 2025-01

📝 How to Use

Enter Initial Investment

Input your starting principal amount.

💡 Starting small is okay - consistency matters!

Set Annual Return Rate

Enter expected annual return rate (%).

💡 Stock funds average 7-10%, savings 2-4%.

Choose Investment Period

Enter how many years you plan to invest.

💡 Compound effect accelerates after 10 years!

Add Monthly Deposits (Optional)

If you plan to add money monthly, enter the amount.

💡 Regular contributions maximize compound growth.

🎯 Who is this for?

Useful for various situations

👶

College Fund for Kids

Start when your child is born to comfortably cover tuition costs.

Long-termEducation

🏠

Down Payment Savings

Calculate how long it takes to save for your dream home.

HomeSavings

🧓

Retirement Planning

Starting in your 30s makes comfortable retirement possible.

PensionRetirement

💎

Investment Simulation

Compare expected returns from ETFs, funds, and savings accounts.

ComparisonETF

💡

Expert Tip

The key to compound interest is 'time'. If you start investing $300/month at 30, someone starting at 40 can't catch up even with $1,000/month. The best time to invest was 10 years ago. The second best time is now.

— Warren Buffett's Investment Philosophy

❓ Frequently Asked Questions

How do I use the compound interest calculator?

Just enter your initial investment, annual return rate, and investment period. Optionally, you can add monthly contributions. The calculator shows your final amount, total interest, and yearly growth chart.

💡 Adding monthly deposits supercharges your compound growth!

What is the Rule of 72?

Divide 72 by your annual return rate to estimate how long it takes to double your money. For example, at 8% return: 72÷8=9 years to double your investment.

💡 Our calculator automatically shows you the Rule of 72 result!

What is the difference between simple and compound interest?

Simple interest applies only to principal, while compound interest applies to principal + accumulated interest. $10,000 at 5% for 20 years: simple interest = $20,000, compound = $26,500. The longer you invest, the bigger the difference.

💡 This is why compound interest is called "interest on interest"!

What is a realistic annual return rate?

It varies by investment: Savings 2-4%, Bonds 3-5%, Stock ETFs 7-10%, Individual stocks vary widely. For long-term planning, 7% is a conservative and realistic estimate.

💡 Remember: higher returns usually mean higher risk!

How early should I start investing?

The earlier, the better! Starting at 25 with $200/month at 7% gives you ~$550,000 by 65. Starting at 35 with the same amount yields only ~$250,000. A 10-year difference makes more than 2x difference!