📈 Compound Interest & Dividend Reinvestment Calculator
See how your investments grow with compound interest and dividend reinvestment — free, instant, no signup.
Project how your investments grow over time with compound interest. Include monthly contributions and optional dividend reinvestment mode. Enter initial amount, monthly contribution, interest rate, and time horizon. The calculator shows total balance, contributions, and interest earned with interactive chart views. All calculations run locally in your browser.
📋 When to Use the Compound Interest Calculator
Investors and retirement planners use the Compound Interest Calculator to project long-term portfolio growth under different contribution levels, interest rates, and compounding frequencies. Switch to Dividend Reinvestment (DRIP) mode to factor in dividend-paying stocks — set your annual yield and dividend frequency to see how reinvested dividends compound alongside price appreciation. Financial educators demonstrate the power of early investing by showing how the same monthly contribution grows dramatically over 20 vs. 30 years. ⚠️ This tool provides mathematical projections based on constant-rate assumptions — actual investment returns vary, past performance does not guarantee future results, and this is not financial advice.
⚙️ How the Compound Interest Calculator Works
The calculator simulates growth month by month. Starting with your initial principal P, each month it adds your contribution M, then applies compound interest: balance += balance × (r/n) where r is the annual rate and n is compounding frequency (12=monthly, 4=quarterly, 1=annual). In DRIP mode, dividends are modeled as additional periodic returns: dividend = portfolio × (yield / divFreq), reinvested immediately to buy more shares. The simulation runs for your chosen number of years, producing month-by-month data for the line and stacked-bar Chart.js visualizations. All computation uses client-side JavaScript — nothing is transmitted.
How to Use the Compound Interest Calculator
- Enter your initial investment amount, monthly contribution, annual interest rate, and time period.
- Select the compounding frequency: monthly, quarterly, or annually.
- View your total balance, total contributions, and total interest earned in the results cards.
- Toggle between chart views (balance growth, contributions vs interest) to visualize your investment growth.
Frequently Asked Questions
How is compound interest calculated?
The Compound Interest Calculator uses the compound interest formula: A = P(1 + r/n)^(nt) + monthly contributions with compounding. Interest is calculated on both your principal and accumulated interest, creating exponential growth over time.
What's the difference between monthly and annual compounding?
Monthly compounding calculates interest 12 times per year, giving you slightly higher returns than annual compounding (once per year) because you earn interest on interest more frequently. The difference grows with larger balances and longer time periods.
How accurate are the projections?
The calculator assumes a constant annual interest rate, which is simplified. Real investment returns fluctuate. Use these projections as estimates and consider running scenarios with conservative rates.
Can I account for taxes or inflation?
This calculator shows gross returns before taxes and inflation. For inflation-adjusted results, subtract your expected inflation rate from the interest rate. For tax considerations, multiply the interest earned by (1 - tax rate).