How to Use
Enter the principal — the starting amount you are investing or saving.
Enter the annual interest rate as a percentage (e.g. 5 for 5%).
Enter the time period in years (decimals accepted, e.g. 2.5).
Select how often interest is compounded each year.
Optionally enter a regular contribution added each compounding period.
Results update automatically — see the final balance, interest breakdown, and growth chart.
The Compound Interest Formula
The calculation relies on the standard formula A = P(1 + r/n)^(nt) + PMT[((1 + r/n)^(nt) - 1) / (r/n)]. In this equation, P represents the initial principal, r is the annual interest rate expressed as a decimal, n denotes the number of compounding periods per year, and t is the total time in years. The term PMT accounts for any regular contributions added at the end of each period. This structure ensures that interest accumulates on both the original balance and the previously earned interest, creating an exponential growth curve over time.
Step-by-Step Calculation Example
- Inputs: Principal = 5,000 | Rate = 6% | Time = 10 years | Compounding = Monthly | Contribution = 100/month
- Monthly rate = 0.06 / 12 = 0.005 | Total periods = 120
- Principal growth = 5,000 x (1.005)^120 = 9,096.98
- Contribution growth = 100 x ((1.005)^120 - 1) / 0.005 = 16,387.93
- Final balance = 9,096.98 + 16,387.93 = 25,484.91
- Total invested = 5,000 + (100 x 120) = 17,000 | Total interest = 25,484.91 - 17,000 = 8,484.91
- Effective annual rate = (1.005)^12 - 1 = 6.1678%
When To Use This Calculator
- Estimating the future value of a savings account or certificate of deposit over a specific timeframe
- Projecting the growth of a retirement portfolio with monthly contributions
- Comparing two bank accounts that offer different compounding frequencies like daily versus quarterly
- Determining the time required to reach a specific savings goal given a fixed interest rate
- Visualizing the impact of increasing contribution amounts on long-term wealth accumulation
Key Features
Recurring Deposit Modeling
Project savings growth by adding fixed amounts to principal at specific compounding intervals.
True Annual Yield Calculation
Convert nominal rates to effective annual percentages for direct comparison across different compounding schedules.
Year-by-Year Projection Table
Display a chronological list of balances, interest earned, and total contributions for every period.
One-Click PDF Export
Generate a static document containing the summary metrics and full projection table for offline sharing.
Privacy And Security
This tool runs entirely in your browser. All calculations and data processing happen locally on your device. No personal information or financial data is sent to any server.
Frequently Asked Questions
What is compound interest?
This calculator projects your investment growth by applying interest to both your starting principal and previously earned interest. All math happens instantly in your browser, so your data never leaves your device. An interactive line chart updates in real time to show exactly how your balance grows over the selected period.
What does compounding frequency mean?
You choose how often interest gets added to your balance, such as daily, monthly, or annually. Higher frequencies like daily compounding generate slightly higher final balances than annual compounding at the same rate. The tool automatically adjusts the periodic rate to ensure every year-by-year breakdown matches your specific schedule.
How does the regular contribution work?
The system deposits your specified contribution amount at the start of each compounding period before calculating interest. For instance, a $100 monthly deposit enters the account before the monthly interest rate applies to the total. This feature lets you model savings plans and recurring investment strategies with exact precision.
What is the effective annual rate (EAR)?
The tool converts your selected compounding frequency into an equivalent annual rate to reveal your true investment return. This metric lets you compare different scenarios directly, whether interest compounds monthly, quarterly, or daily. The calculator displays this value automatically so you can evaluate the actual performance of your savings plan.
Can I enter fractional years?
Yes, the calculator accepts decimal values for the time period to model partial years accurately. You can enter 0.5 for six months or 2.25 for two years and three months to refine your projections. The system processes these fractional inputs to generate a precise final balance and total interest earned.