Compound Interest Calculator
Calculate how your investments grow over time with the power of compound interest. Plan for retirement, savings goals, or any long-term financial target.
Investment Details
Enter your investment details
to see projected growth
How to Use This Calculator
This compound interest calculator offers 4 calculation modes to help you plan various investment scenarios. Select the mode that matches your goal and enter your values to see instant results.
Future Value
Calculate how much your investments will grow over time.
Example: “$10,000 + $500/month at 7% for 20 years”
Time Needed
Find out how long it takes to reach your goal.
Example: “How many years to reach $100K?”
Required Return
Calculate the return rate needed to hit your target.
Example: “What return do I need to reach $500K in 15 years?”
Monthly Investment
Find out how much you need to invest each month.
Example: “How much monthly to reach $1M in 30 years?”
Compound Frequency
Select how often interest is calculated and added back to the principal.
| Frequency | Explanation | Example |
|---|---|---|
| Annually | Interest calculated once a year | Bonds, CDs |
| Monthly | Interest calculated monthly (Default) | Savings, ETFs |
| Daily | Interest calculated daily | High-Yield Savings |
Example: $10,000 for 10 years at 7%: Annually: $19,672 vs. Monthly: $20,097.
Quick Start Presets
Use the buttons at the top for common scenarios:
- $500/mo / 20y: Long-term investment plan.
- $100k Goal: Calculate savings needed for $100k.
- $1M Retire: Plan for a $1 million retirement fund.
Understanding Your Results
- Power of Compounding: See exactly how much more you earn with compound vs simple interest.
- Growth Chart: Visualize how your investment grows year by year.
- Principal vs Earnings: See what portion of your final balance is contributions vs growth.
- Share Your Results: Copy your calculation URL to save or share with others.
🌏 Compare with Other Calculators
Check out our Korean won-based calculator for domestic investments.
Compound Interest FAQ
Compound interest is interest calculated on both the initial principal and the accumulated interest from previous periods. Unlike simple interest (which only earns on the principal), compounding creates exponential growth over time. Einstein reportedly called it 'the eighth wonder of the world.'
The S&P 500 has averaged about 10% annually since 1957 (before inflation). After adjusting for inflation, real returns are approximately 7%. For conservative planning, many financial advisors use 6-7%. High-yield savings accounts currently offer 4-5%.
The Rule of 72 is a quick way to estimate how long it takes to double your money. Divide 72 by your annual return rate. At 7% returns, your money doubles in about 10 years. At 10%, it doubles in about 7 years.
Historically, lump sum investing beats dollar-cost averaging (DCA) about 2/3 of the time because markets tend to go up. However, regular monthly contributions are practical for most people, reduce timing risk, and build investing discipline.
Accounts like 401(k)s, IRAs, and Roth IRAs let your investments compound without annual tax drag. In a taxable account, you might lose 15-20% of gains to taxes each year. Tax-advantaged accounts let 100% of your returns compound, significantly boosting long-term growth.
At a 7% annual return: invest $1,000/month for 30 years to reach ~$1.2M. Starting with $50,000 and adding $500/month reaches $1M in about 28 years. Use our 'Required Monthly' mode to calculate your exact numbers.