Compound Interest Calculator
Want to see how your savings grow? Enter your starting amount, interest rate, and time horizon. Add regular contributions to see the power of compound interest in action.
The Magic of Compound Interest
Albert Einstein supposedly called compound interest the eighth wonder of the world. The math is simple but the results are remarkable. When your interest earns interest, growth accelerates over time without any extra work from you.
Here's how it works: You invest $10,000 at 7% annual interest. After one year, you have $10,700. In year two, you earn 7% on $10,700, not just the original $10,000. That gives you $11,449. Each year the base grows, so the interest dollars grow too.
Over 30 years at 7%, that $10,000 becomes $76,123. You contributed $10,000 and earned $66,123 in interest. The longer your money compounds, the more dramatic the effect becomes. Time is the most powerful variable in the equation.
Why Regular Contributions Matter
Adding money regularly supercharges compound interest. Even small monthly contributions add up. Put in $200 per month for 30 years at 7%, and you'll have over $240,000. Your contributions total $72,000, but you earn $168,000 in interest.
Many people wait to invest until they have a large sum. That's a mistake. Starting early with small amounts beats starting late with large amounts. A 25-year-old who invests $200 monthly until age 65 will likely end up with more than a 40-year-old who invests $500 monthly until 65, assuming identical returns.
Automate your contributions so you never miss a month. Treat investing like a bill you must pay. The consistency matters more than the amount, especially in the early years when you have the most time for compounding to work.
Compounding Frequency Explained
Compounding frequency determines how often interest is calculated and added to your balance. Annual compounding adds interest once per year. Monthly compounding adds it 12 times per year. Daily compounding adds it 365 times.
More frequent compounding is better, but the difference is smaller than most people think. On a $10,000 investment at 7% for 20 years, annual compounding gives you $38,697. Daily compounding gives you $40,256. That's $1,559 more, or about 4% better.
Most savings accounts compound daily. Investment accounts effectively compound whenever you earn dividends or interest, which varies by holding. The key insight is that compounding frequency matters less than the interest rate and time horizon. Focus on getting a good rate and staying invested for the long haul.
Frequently Asked Questions
What is compound interest?
Compound interest is interest earned on both your principal and previously earned interest. Instead of earning interest only on your initial deposit, you earn interest on interest, creating exponential growth.
How often should interest compound?
More frequent compounding produces slightly higher returns. Daily compounding beats monthly, which beats quarterly. The difference is small but adds up over decades.
What's a realistic interest rate to use?
Savings accounts average 0.5-5%. Index funds historically return 7-10% annually. Use conservative estimates for long-term planning.
Does this account for inflation?
No. The calculator shows nominal returns. To find real returns, subtract the inflation rate (typically 2-3%) from your interest rate.
Can I lose money with compound interest?
If your investment loses value, compound losses work against you the same way compound gains work for you. This calculator assumes positive returns.