Compound Interest Calculator
Visualize the power of compounding on your savings and investments. Enter your starting balance, monthly contributions, and expected interest rate to see your wealth grow over time. Features a detailed year-by-year breakdown and a comparison between your contributions and the total interest earned over the decades.
About the Compound Interest Calculator
Discover the power of compounding over time. Calculate how your initial investment and regular contributions grow exponentially through the magic of compound interest.
How does this calculator work?
This tool uses up-to-date mathematical formulas and tax rates to provide an accurate estimate. It runs completely in your browser using JavaScript, meaning your financial data is never sent to our servers. Simply enter your numbers into the inputs above, and the calculations will update instantly.
Why use this tool?
Financial clarity is essential for making good decisions. Whether you are budgeting for the month, estimating your tax liability, or planning for retirement, our calculators give you the precise numbers you need without having to rely on complex spreadsheets.
What Is This Calculator?
A compound interest calculator shows you how money grows when interest is earned not just on your initial deposit but also on the interest already accumulated. Einstein reportedly called compound interest the "eighth wonder of the world." The core formula is A = P(1 + r/n)^(nt), where P is principal, r is annual rate, n is compounding frequency, and t is time in years.
When Should You Use This Tool?
- You are planning a long-term savings goal such as retirement or a house deposit
- You want to compare savings accounts with different interest rates
- You are evaluating whether to invest a lump sum or contribute monthly
- You want to see the real impact of starting investing 5 or 10 years earlier
- You are a student or parent planning for education costs over time
How This Calculator Works
Formula Used
A = P(1 + r/n)^(nt) + PMT × [((1 + r/n)^(nt) − 1) / (r/n)]
Assumptions & Limitations
- P = Principal, r = Annual rate (decimal), n = Compounding periods/year, t = Years, PMT = Periodic contribution
- Contributions assumed at the start of each compounding period
- Interest rate held constant for the entire projection period
- Does not account for taxes on interest income or capital gains
Data Source
Standard compound interest formula (IRS Publication 550) · Last verified: May 2026