What this calculator shows you
- See Future Value
- Project your investment growth over any time period
- Compare Scenarios
- Test different interest rates and contribution amounts
- Visualize Growth
- Interactive charts show your wealth building over time
- Save Calculations
- Create an account to save and compare multiple scenarios
What is Compound Interest?
Compound interest is often called the "eighth wonder of the world" for good reason. Unlike simple interest, which only earns on your principal, compound interest earns interest on both your principal AND your previously earned interest. This creates exponential growth over time, making it one of the most powerful tools for building wealth.
The Compound Interest Formula
The formula for compound interest is 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 compounds per year, and t is the time in years. Understanding this formula helps you see why starting early and compounding frequently makes such a big difference.
How Compounding Frequency Affects Your Returns
The more frequently interest compounds, the more you earn. Daily compounding earns more than monthly, which earns more than annually. For example, $10,000 at 5% for one year grows to $10,500.00 with annual compounding, $10,511.62 with monthly, and $10,512.67 with daily. The jump from annual to monthly matters far more than monthly to daily, and the gap widens over decades.
The Power of Starting Early
Time is the most crucial factor in compound interest. At a 7% average annual return, someone who invests $5,000 annually from age 25-35 (10 years) and stops will have more at 65 (about $563,000) than someone who invests $5,000 annually from age 35-65 (30 years, about $505,000). The early starter contributed $50,000 vs $150,000, but time did the heavy lifting.
Strategies to Maximize Compound Interest
To maximize compound interest: 1) Start investing as early as possible, 2) Reinvest all dividends and interest, 3) Choose investments with higher returns when appropriate for your risk tolerance, 4) Make regular contributions to keep adding to your principal, 5) Be patient and let time work its magic.
Questions people ask
What is a good compound interest rate?
The S&P 500 returned about 10% a year before inflation from 1928 to 2023 (NYU Stern historical returns data). Savings and CD rates change often: the FDIC national average was 0.38% for savings and 1.76% for a 12-month CD in October 2026, and top online banks pay more, so check current rates. The "best" rate depends on your risk tolerance and investment timeline.
How often should interest compound?
More frequent compounding means higher returns. Daily compounding is ideal, followed by monthly, quarterly, and annually. Most savings accounts compound daily, while many investments compound based on when dividends are paid.
Is compound interest the same as APY?
APY (Annual Percentage Yield) accounts for compound interest and shows your actual annual return. APR (Annual Percentage Rate) is the simple interest rate. APY is always equal to or higher than APR due to compounding.
Education only, not personalized financial, tax or investment advice. Results are estimates based on the numbers you enter; real returns vary and losses happen.