Compound Interest Calculator
Visualize exponential growth when interest earns interest daily, monthly, or annually.
Parameters & Inputs
Summary & Breakdown
About the Compound Interest Calculator
Albert Einstein famously called compound interest the eighth wonder of the world. Because interest generates its own interest with each compounding cycle, your balance grows along an upward curved exponential trajectory rather than a flat line.
This calculator models compound interest with regular recurring contributions, contrasting principal contributions against interest earned.
Witnessing the hockey-stick curve encourages disciplined saving and long-term investment patience.
How the Calculations Work
Calculates future value combining compound lump sum and periodic monthly deposits.
A = P(1 + r/n)^(nt) + PMT * [((1 + r/n)^(nt) - 1) / (r/n)]
Variables & Definitions
- P: Initial principal deposit
- PMT: Regular monthly contribution
- r: Annual interest rate as decimal
- n: Compounding cycles per year
- t: Time elapsed in years
Starting with $5,000, depositing $250 monthly for 15 years at 8.0% compounded monthly: Total deposits equal $50,000 ($5,000 + $45,000). Total interest earned is $49,552, doubling your invested capital.
Key Terms Explained
Exponential Growth
Growth whose rate becomes ever more rapid in proportion to the growing total number.
Principal
The baseline capital invested out of pocket, excluding all investment gains.
Compounding Period
The time span between successive interest credit dates.
Nominal vs Real APY
Nominal APY reflects compounding before inflation; real APY reflects purchasing power gain.
Practical Tips & Pitfalls to Avoid
Lengthen your time horizon
Compounding achieves its most rapid dollar growth in year 20+, not year 2.
Never disrupt compounding
Frequent trading, market timing, or early withdrawals halt exponential compounding in its tracks.
Increase contributions slightly
Adding $50 extra per month compounds into tens of thousands of extra dollars over 20 years.
Reinvest all payouts
Ensure all bond coupons and equity dividends are enrolled in automatic dividend reinvestment (DRIP).
Frequently Asked Questions
Simple interest earns returns strictly on the initial deposit. Compound interest earns returns on both initial principal and all accumulated interest.
Yes. Daily compounding yields slightly more than monthly or annual compounding because returns are reinvested sooner.
Your balance grows to $99,552, with interest ($49,552) almost matching total cash contributed ($50,000).
Divide 72 by the annual interest rate to determine approximately how many years it takes for an investment to double.
Yes. On credit card debt and revolving loans, compound interest works against you, compounding debt balances outward.